EP0348436A1

EP0348436A1 - Thread-cutting device for zig-zag sewing machines.

Info

Publication number: EP0348436A1
Application number: EP88903802A
Authority: EP
Inventors: Ernst Albrecht; Harald Dinges
Original assignee: Pfaff Industriemaschinen GmbH
Current assignee: GM Pfaff AG
Priority date: 1987-05-09
Filing date: 1988-04-19
Publication date: 1990-01-03
Anticipated expiration: 2008-04-19
Also published as: KR890700708A; JP2912374B2; US5005504A; JPH02503389A; KR950012454B1; BR8807499A; ES2007485A6; EP0348436B1; DE3715603C1; WO1988008894A1

Abstract

La lame (28) de coupe-fil est mobile sur un plan parallèle à l'attrape-fil (33) et reliée par un mécanisme de transmission (45 à 58) à sections d'arrêt (54, 55) avec l'entraînement de l'attrape-fil (33) de façon à pouvoir se déplacer avec ce dernier jusqu'à la position de coupe au-dessous du centre du trou de l'aiguille. Pendant que la lame (28) du coupe-fil reste stationnaire dans la position de coupe, l'attrape-fil achève l'opération de séparation des fils. La lame (28) du coupe-fil ne se déplace en arrière qu'une fois que les fils ont été sectionnés pendant le mouvement en arrière de l'attrape-fil (33). Le mécanisme (45 à 58) de transmission de la lame (28) du coupe-fil est craboté, ce qui permet de sectionner de manière fiable même de gros fils.The wire cutter blade (28) is movable on a plane parallel to the wire catcher (33) and connected by a transmission mechanism (45 to 58) with stop sections (54, 55) with the drive of the thread catcher (33) so that it can move with the latter to the cutting position below the center of the needle hole. While the thread cutter blade (28) remains stationary in the cutting position, the thread catcher completes the thread separation operation. The thread cutter blade (28) only moves back once the threads have been cut during the backward movement of the thread catcher (33). The mechanism (45 to 58) for transmitting the blade (28) of the thread cutter is clutched, which makes it possible to reliably cut even large wires.

Description

Fadeπschneidvorrichtung for zigzag sewing machines

A thread cutting device according to the preamble of claim 1 is known from DE-GM 1 968 920. In this thread cutting device, the 5 cutting blade cooperating with the cutting edge of the thread catcher is fastened to the underside of the throat plate at a lateral distance from the la-hole-shaped stitch hole.

Since the needle in zigzag sewing has a greater distance from the stationary cutting knife in one 1 ° stitch position than in the other, thread lengths of uneven length result on the material to be sewn, the shortest thread ends on the cutting knife facing and the longest thread ends on the cutting knife 15 opposite stitch position are formed.

From DE-PS 31 24 795 a further thread cutting device for zigzag sewing machines is known, in which the thread catcher to achieve one of

_2θ the needle position of the needle independent length of the needle thread end connected to the needle and the thread supply on its side opposite the barb, a second barb for the leg of the needle thread loop leading to the needle

25. However, the arrangement of the second barb has no influence on the length of the thread ends on the material to be sewn, ie, the length thereof, as in the first thread cutting device, depends on the last insertion position of the needle. Finally, by DE-PS 17 60 703 a Fadeπschπeidvorrichtuπg for

Double chain stitch sewing machines are known which have a fade catcher movable parallel to the throat plate plane with a cutting edge as well as a cutting knife arranged parallel to the same and movable in the same direction and a thread clamp movable with the cutting knife. The Fadeπfäπger is provided with a pin, which is in engagement with a longitudinal slot of the cutting knife and the Fadεπklemme so that the cutting knife and the thread clamp are each carried by the thread catcher from the rest position to the working position and vice versa when the pin the whole Length of the longitudinal slots. To prevent the cutting knife and the thread clamp from moving prematurely and in an uncontrolled manner, they are replaced by one

Spring detent held in their two end positions.

Apart from the fact that this thread cutting device is not for double lockstitch - but for

Double chain stitch sewing machines was designed, which also do not serve for the production of zigzag seams but straight stitch seams, it is also not suitable for cutting through thick and tear-resistant threads, which oppose the cutting with such a high resistance that .the force to be cut is greater than the holding force of the spring catch. In this case, namely, the cutting knife would be pushed out of the cutting position actually provided close to the tap hole before the threads were completely severed, and the cutting process would only be in the idle position of the cutting knife relatively far away from the tap hole accomplished. In this way there would be undesirably long thread ends on the sewing material.

The invention has for its object to provide a thread trimmer for zigzag sewing machines so that regardless of the stitch position of the last stitch, uniformly short thread ends are achieved on the workpiece. This object is achieved by the characterizing features of claim 1.

As a result of the measure of moving the cutting knife into a cutting position below the center of the overstitch width and thus the center of the longitudinal extension of the tap hole, the leg of the needle thread loop and the looper thread on the workpiece side are always cut off at a particularly short distance from the workpiece. The overstitch position of the last stitch has no significant influence. on the cutting result, so that essentially the same short fades are always achieved.

By the measure according to claim 2, the cutting knife to connect via a positive gear with the drive of the thread catcher, an inevitable coupling of the movement of the thread catcher with that of the cutting knife is achieved, thereby increasing cutting resistance, as z. B. when cutting thick and tear-resistant threads can reliably be overcome.

In claim 3, an advantageous structural design of the fade cutting device is specified. To place the needle plate by the measure, the thread catcher that Schπeidmesser and angle lever on ^", it is possible that Fadenschneidvorrichtuπg can also be retrofitted to sewing machines that have already been delivered.

The design of the thread catcher specified in claim 4 brings in connection with the particularly short workpiece ends thread ends improved sewing security at the beginning of the next sewing process. This is done in such a way that immediately after the penetration of the separating tip of Fadeπfängers in the ⁰ needle thread loop of the needle-side loop leg from Haltefiπger, that is detected by the incision between Haltefiπger and separator finger and thereby already tightened by Nadelfadeπvorrat during further division process thread. If in the further course of the gripper the needle thread loop around the

Has passed around the bobbin case, the gripper thread and the workpiece-side leg of the needle thread loop are behind the barb of the thread catcher. The needle thread then runs from the barb under the thread catcher 0 as a needle-side loop leg to the

Incision between holding and separating finger, whereupon it then rises to the tap hole. Since the needle-side loop leg does not rise from the barb directly to the tap hole but makes the detour via the incision between the holding and separating finger, after thread cutting the needle-side thread end is longer by the amount of the detour and thus the sewing reliability is increased accordingly.

° The invention is explained with reference to an embodiment shown in the drawing. It shows:

Figure 1 is a partially sectioned view of part of a sewing machine with the 5 Fadeπschπeidvorrichtung. Figure 2 shows a part of the drive mechanism us the Fadeπschneidvorrichtung.

3 shows a diagrammatic representation of the throat plate and the thread cutting device with a view from below of the device parts;

Fig. 4 is a partially sectioned graphical

Representation of the thread catcher, the cutting knife and the throat plate;

Fig. 5 the thread course immediately -.- before

Cut through, the last stitch formed in the left stitch position;

Fig. 6 shows the course of the thread corresponding to Fig. 5 but with the right stitch position.

The sewing machine has a housing (1) which consists of a carrier plate (2), a base (3), a support arm (4), a stand (5) and an arm (6) which is fitted into a head (7) expires. An arm shaft (8) is mounted in the arm (6) and drives a needle bar (11) via a crank (9) and a link (10). A thread-guiding needle (12) is fastened in the needle bar (11).

The needle bar (11) is received in a frame (13) which is displaceably mounted on a bolt (14) running parallel to the longitudinal axis of the arm (6) and is connected to a push rod (15) running parallel to it. The push rod (15) forms the output member of a known zigzag stitch actuator, not shown. Such a stitch regulator is shown and described for example in DE-PS 33 20 158.

The needle (12) works together to form double lockstitches with a double-rotating gripper (16) which is arranged in the support arm (4) and which contains a rotating gripper body (17) and a fixed bobbin case (18). A throat plate (19) is arranged in the support arm (4) above the gripper (16) and has a stitch hole (20) for the passage of the needle (12).

On the support arm (4) a sewing material holder (21) is arranged, which has a lower clamp jaw (22) and an upper clamp jaw (23). The upper

Klammerbackeπ (23) contains a spring-loaded

Holding plate (24), which is in a known manner via a

Roller lever (25) and a substantially vertically movable pressure plate (26) can be lifted off the lower clamp jaw (22). The feed movements of the material holder (21) and the setting of the zigzag stitch actuator are controlled by a cam, not shown, as is disclosed in the aforementioned DE-PS 33 20 158.

A cutting knife (28) designed as a flat slide is slidably arranged in a flat guide groove (27) provided on the underside of the throat plate (19) in the region of the stitch hole (20) and parallel to the circumferential plane of the gripper (16). The cutting knife (28) contains a rectangular recess (29), the lower left-hand limitation border of which, according to the drawing, forms a cutting edge (30). The cutting knife (28) is screwed onto the throat plate (19) by ^" two Guide pieces (31) held against falling.

The guide pieces (31), each with a step-shaped recess (32), together form a guide for a thread catcher (33) designed as a flat slide, which rests directly on the underside of the cutting knife (28) and, like this, parallel to the circumferential plane of the gripper (16) is movable. The right end according to the drawing, always outside the guide pieces (31), the end region of the

Fadeπfεngers (33) is curved upwards by a small amount and runs out into an essentially centrally located elongated separating tip (34). A short holding finger (35) is provided at a small lateral distance from the separating tip (34), as a result of which an incision (36) is formed between the separating tip (34) and holding finger (35), which has a groove-like shape.

The Fadeπfäπger (33) has in its upwardly curved section a laπglochartig, essentially longitudinal recess. (37), whose end facing the separating tip (34) lies in the apex plane of the curved section _t, as a result of which the semicircular upper beginning of the recess (37) forms a cutting edge (38). In the thread catcher (33) there is also a recess (39) extending obliquely in the direction of the recess (37), whereby a barb (41) is formed in connection with the longitudinal edge (40). At the end of the thread catcher (33) opposite the separating tip (34), two tabs (42, 43) bent downwards form a guide for a ball pin (44) of a drive lever (45) which is secured to the throat plate (46) by a collar screw (46). 19) is stored.

The drive lever (45) is connected via a hinge pin (47) to a pull rod (48), the opposite end of which is bent downwards. The pull rod (48) has a longitudinal, straight guide slot (49) in the cranked section and carries a short, upwardly projecting pin (50). A hinge pin (51), which is fastened to the throat plate (19) and on which a flat angle lever (52) is mounted, engages in the guide slot (49).

A control slot (53) in which the pin (50) engages is provided in the one leg of the angle lever (52), which extends between the cranked section of the pull rod (48) and the throat plate (19). The control slot (53) is divided into two standstill sections (54, 55) and a movement section (56) arranged between them. At the end of the other leg of the winding lever (52) there is an elongated hole (57) into which a pin (58) attached to the cutting knife (28) engages.

One end of a pull rod (59), the other end of which is connected to a carrier (60), engages on the pivot pin (47) of the drive lever (45). The carrier (60) is fastened on a rotatably mounted and axially displaceable sliding rod (61). On the slide rod (61), a scanning lever (62) is attached, which has a cam follower (63). A preloaded leg spring (64) arranged on the slide rod (61), one end at one Rib of the base (3) and at the other end is attached to the carrier (60), exerts a counterclockwise torque as shown in FIG. 2 on the slide rod (61).

^' 5

The scanning lever (62) interacts with a cam disk (65) which has a cam groove (66) and is fastened on a shaft (67). The shaft (67) is connected to the arm shaft (8) via a toothed gear (68)

10 drive connection. The scanning lever (62) is a

Electromagnet (69) (Fig. 2) assigned, which acts on the pull rod (70) arranged pressure piece (71) on the underside of the scanning lever (62).

15 The scanning lever (62) is also assigned a pawl (72) which has two stepped shoulders (73, 74) and is arranged on a shaft (75) in a rotationally fixed manner. A prestressed leg spring (76) arranged on the shaft (75), which is at one end on a rib of the

²⁰ base (3) and at the other end on the pawl (72), exerts on the shaft (75) a torque corresponding to FIG. 2 clockwise.

A three-armed lever (78) 25 is arranged on a shaft (77) in a rotationally fixed manner. There is one on one arm

Switch rod (79) articulated, which has a guide slot (80) in which a housing-fixed pin (81) engages. At the free end of the shift rod (79) a wedge-shaped extension ('82) is formed, which cooperates with an appropriately designed extension (83) of the locking pawls (72). On another arm of the lever (78) is a tie rod

(84) articulated, which is connected via a lever mechanism (not shown) to the pressure plate (26) in such a way that when the lever (78) is pivoted counterclockwise as shown in FIG. 1, the pressure plate (26) moves downward and as a result of which the holding plate (24) of the upper clamp jaw (23) is raised. An electromagnet is used to carry out the pivoting movement of the lever (78)

(85), which acts on the third arm of the lever (78) via a pressure piece (87) arranged on its pull rod (86).

A one-armed drive lever (88) is also attached to the shaft (77). A free shoulder (89) formed on the scanning lever (62) is assigned to the free end of the drive lever (88).

functionality

Several stitches before the end of a seam, the speed of the sewing machine is reduced to the so-called cutting speed, from which the sewing machine can be stopped practically without delay.

During the last stitch formation process of a seam, approximately at the time when the needle (12) is pulled out of the stitch hole (20), the electromagnet (69) is acted upon, after which it moves the scanning lever (62) from the position shown in FIG. 2 pivots upwards and thereby swivels the cam follower (63) into a standstill section of the cam groove (66) which runs without an incline and is not designated in any more detail. Up to this point, the thread catcher (33) and the cutting knife (28) are in the rest position with a lateral distance from the tap hole (20). When the raised position of the scanning lever (62) is reached, the leg spring (76) pivots the pawl (72), based on FIG. 2, to the right, as a result of which the shoulder (74) slides under the front end of the scanning lever (62) and opens up this way ensures its position.

Shortly after the curve follower (63) has been swiveled into the cam groove (66) of the cam disk (65) rotating in synchronism with the arm shaft (8), a movement section (66a) of the cam groove (66) running in the axial direction becomes effective, whereby the cam follower ( 63) and the scanning lever (62), based on FIG. 1, are shifted to the right. The thrust movement of the scanning lever (62) is transmitted to the drive lever (45) via the slide rods (61), the carrier (60) and the pull rod (59), whereby the drive lever (45) executes a pivoting movement.

Due to the pivoting movement of the drive lever (45), the thread catcher (33) and the pull rod (48), based on FIG. 3, are shifted to the right into their end position shown in this figure. The separating tip (34) penetrates into the needle thread loop formed by the gripper (16), its leg (NW) leading to the sewing material (W) and the hook thread (G) coming into contact with the longitudinal edge (40), while the needle (12) leading leg (NN) from the Begreπzuπgskante of

Incision (36) between the separating tip (34) and the holding finger (35) is detected. In the further course of the catcher or gripper movement, the needle thread loop is completely guided around the spool capsule (18) by the gripper (16) and the thread catcher (33) penetrates so far the needle thread loop until the thread leg (NW) leading to the sewing material (W) and the looper thread (G) slide off the longitudinal edge (40) and reach behind the barb (41) into the recess (39).

During the forward movement of the thread catcher (33), the thread is withdrawn from the needle thread supply. After the gripper (16) has guided the needle thread loop around the spool capsule (18), it is used by the known thread feeder, not shown

The sewing machine is pulled upwards, laying itself around the thread catcher (33) such that the needle-side loop leg (NN) from the tap hole (20) via the incision (36) and the two cutouts (39 and 37) to the cutting edge (38) and the workpiece-side loop leg (NW) runs from the cutting edge (38) to the tap hole (20).

Due to the simultaneous movement of the thread catcher (33), the displacement of the pull rod (48) moves with the guide slot (49) relative to the fixed hinge pin (51), the pin (50) being displaced within the control slot (53). As long as the pin (50) moves within the standstill section (54) which runs essentially parallel to the longitudinal axis of the tension lever (48), the position of the angle lever (52) remains unchanged and the cutting knife (28) remains in its rest position, in which it Cutting edge (30) has a lateral distance to the tap hole ° (20). As soon as the pin (50) in the

Movement section (56) occurs, it causes a pivoting of the angle lever (52) and thus a displacement of the cutting knife (28), this movement taking place essentially synchronously with the movement of the fade pin ⁵ (33). If the pin (50) the end of the Has reached the movement section (56), the cutting edge (30) is below the center of the tap hole (20), the cutting knife (28) having reached its cutting position. During the subsequent movement of the pin (50) within the standstill section (55), the winding lever (52) remains unchanged in its new position, whereby the cutting knife (28) also remains in the cutting position.

The sewing machine is stopped shortly after the top dead center of the needle movement. Here, the cam follower (63) is located at the apex of the movement section (66a) which is arc-shaped in the axial direction, the thread catcher (33) and the pull rod (48) having reached their right-hand end position in relation to the drawing.

After the sewing machine is stopped, the electromagnet (85) is acted upon, whereupon it pivots the three-armed lever (78) and the drive lever (88), based on FIG. 1, counterclockwise. Because of this pivot movement, the pressure plate (26) is actuated via the pull rod (84) and the holding plate (24) is raised. At the same time, the shift rod (79), based on FIG. 1, is pulled to the right and the pawl (72) is pivoted back against the action of the leg spring (76) via the wedge-shaped extension (82), which interacts with the extension (83) , whereupon the leg spring (64) pivots the scanning lever ^' (62) downward again and thereby removes the cam follower (63) from the cam groove (66). As soon as the cam follower (63) is out of engagement with the cam groove (66), the free end of the drive lever (88) rests against the shoulder (89) and then shifts the scanning lever (62) axially Direction back to the starting position shown in Fig. 1.

This push-back movement of the scanning lever (62) is transmitted via the pull rod (59) to the drive lever (45), whereupon the latter pulls back the thread catcher (33) and the pull rod (48). Since the pin (50) initially moves within the standstill section (55), the cutting knife (28) remains in the ⁰ cutting position, specifically because of the formation of the control slot (53), until the thread catcher (33) with its cutting edge (38) has slid over the cutting edge (30) of the cutting knife (28) and the needle thread (N) and the looper thread (G) have been penetrated 5 ^.

.After the cutting of the threads of the pin (50) enters the Beweguπgsabschπitt (56) of the control slot (53) and ^"causes characterized in that the angle lever (52) again ⁰ verschweπkt and the cutting knife (28) in its Ruhe¬ or ^' When the pin ^~ (50) subsequently enters the standstill section (54), the cutting knife (28) remains in the previously reached position, while the 5 thread catcher (33) continues to its rest or Starting position is withdrawn, in which the separating tip (34) is completely removed from the area of the tap hole (20).

° As a comparison of FIGS. 5 and 6 shows, the Fadeπschπeidvorrichtuπg according to the invention, regardless of the overstitch position of the last stitch, essentially the same short workpiece ends are formed. In the same way, the length of the 5 _m needle thread end connected to the needle (12) remains respective overstitch position largely unaffected. 5 and 6 can also be seen, the length of the needle thread end connected to the needle (12) depends on the distance of the incision (36) to the opposite boundary edge of the recess (39). The length of this thread end can be varied by appropriately designing the thread catcher (33).

Claims

1. Fadeπschneidvorrichtung on zigzag sewing machines with a stitch plate having a stitch hole, a circumferential lockstitch looper and a fade catcher movable depending on the angular position of the hook shaft, which has a separating tip, a barb for the leg of the needle thread loop leading to the material to be sewn and the hook thread and a cutting edge which, in cooperation with a cutting knife, passes through the threads caught by the barb, characterized in that the cutting knife (28) is movable in a plane parallel to the thread catcher (33) and via a gear (45 to 58)

Standstill sections (54, 55) with its drive connected in such a way that the cutting knife (28) together with the fade catcher (33) from a rest position located to the side of the tap hole (20) with its cutting edge (30) in a region below the center the overstitch width of the cutting position is movable and, after the threads have been separated and separated, can be returned to the rest position together with the thread catcher (33) which moves further after the cutting knife (28) has been brought into the cutting position (33).

2. Thread cutting device according to claim 1, characterized in that the gear (45 to 58) for the cutting knife (28) is designed positively. η.

3. Fadenschπeidvorrichtung according to claim 1 and 2, characterized in that the Fadenfäπger (33) and the cutting knife (28) are arranged and guided by common means (31) on the needle plate (19) and a drive lever (45) of the Fadeπfänger (33) is connected via a tie rod (48) to an angle lever (52) mounted on the throat plate (19) by means of an articulated pin (51), by inserting the articulated pin (51) into a guide slot (49) of the tie rod (48) and one on the tie rod (48) attached pin (50) engages in a control slot (53) of the winding lever (52), and that the angle lever (52) is articulated on the cutting knife (28) via an elongated hole pin connection (57, 58).

4. Thread cutting device according to one or more of claims 1 to 3, characterized in that the Fadeπfäπger (33) on the side facing away from the barb (41) with a lateral distance to the separating tip (34) a holding finger (35) for the needle (12 ) leading leg (NN) of the needle thread loop.