EP0417119B1 - Process for making a seam - Google Patents

Abstract

In a known sewing machine, the needle thread is not actually severed when the griffer thread runs out. Instead, a gap exists between the point of connection of the needle thread with the end of the old gripper thread and that of the needle thread with the new griffer thread. The aim of the invention is therefore to eliminate this weak point in the seam on the side facing the griffer. After a break in, or end of, a thread, the material stitched is moved backward by one stitch length, a new griffer thread is advanced and knotted by at least one stitch with the needle thread in the same stitching hole, in which the old griffer thread is also knotted in correct sequence with the needle thread. The process is suitable for making seams with sewing machines.

Description

The invention relates to a method according to the preamble of claim 1.

From DE-PS 20 28 027 a sewing machine is known, on the housing of which a guide groove is formed close to the gripper, at the end of which is turned away from the gripper a cutting device is arranged. The guide groove is used to hold the thread end of the old hook thread coming from the material and after changing the bobbin to hold the thread start of the new hook thread. After shortening the looper threads running in the guide groove by the cutting device, the sewing process is continued, the new looper thread being knotted with the needle thread at the first stitch and pulled to the stitch formation point, while the old looper thread is gradually pulled out of the guide groove by the feed movement of the sewing material.

Since the needle thread in this sewing machine is not severed when the looper thread has ended, a seam is obtained, the top of which is formed without an interruption. However, since the needle thread is only connected to the old hook thread on the last stitch before changing the bobbin and only the new hook thread on the first stitch after changing the bobbin, the underside of the seam has an interruption that turns out to be a weak point when loaded.

The invention has for its object to provide a method for producing a seam in which the needle thread runs uninterrupted and both the knotting with the old and the knotting with the new looper thread should be safe, so that the strength of the seam is not weakened .

This object is achieved in a method according to the preamble of claim 1 by its characterizing features.

The changeover of the stitch regulator to the reverse stitch after a malfunction of the looper thread causes the sewing material to be moved back relative to the needle to the puncture hole formed before the malfunction of the thread, at which the last properly formed knot with the old looper thread took place. After feeding new looper thread by thread retraction from the bobbin in double lockstitch sewing machines or from an endless thread supply in multi-thread chainstitch sewing machines when thread breaks or after changing the bobbin in double lockstitch sewing machines at the end of the thread, the stitch regulator is set to zero so that the needle thread depends on the The number of stitches that are subsequently executed is knotted once or several times in the same puncture hole with the new hook thread. A multiple knot provides greater security against loosening this knot. Since the old and the new looper thread are knotted next to each other on an almost punctiform surface with the uninterrupted needle thread in the puncture hole, this connection point proves to be just as resilient as the rest of the seam.

After the thread fault has been eliminated, the seam formation is continued by changing the stitch regulator to the forward stitch.

The measure of claim 2 has the effect that the free ends of the old and the new looper thread hanging down from the material to be sewn are shortened to such an extent that when the seam is continued they will certainly not be gripped by the looper and integrated into the seam.

• Fig. 1 eine schaubildliche Darstellung der Verstellund Antriebsteile für den Stoffschieber einer Nähmaschine
• Fig. 2 eine schaubildliche Darstellung der Spulenkapsel
• Fig. 3 wie Figur 2, jedoch die Führung des Fadens darstellend
• Fig. 4 eine Schneidvorrichtung
• Fig. 5 eine Steuervorrichtung
• Fig. 6 Schaubilder zur Darstellung der Verfahrensschritte nach einer Fadenstörung
  • a) Nadel in ihrem unteren Umkehrpunkt im letzten Einstichloch,
  • b) Nadel in ihrem oberen Umkehrpunkt über dem vorletzten Einstichloch,
  • c) Nadel bei ihrer Bewegung zum oberen Umkehrpunkt nach einem erneuten Einstich in das vorletzte Einstichloch,
  • d) Nadel in ihrem oberen Umkehrpunkt über dem vorletzten Einstichloch nach dem erneuten Einstich,
  • e) Nahtbildung wird fortgesetzt.

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

• Fig. 1 is a diagrammatic representation of the adjustment and drive parts for the fabric pusher of a sewing machine
• Fig. 2 is a perspective view of the bobbin case
• Fig. 3 as Figure 2, but illustrating the guidance of the thread
• Fig. 4 shows a cutting device
• Fig. 5 shows a control device
• Fig. 6 diagrams to illustrate the process steps after a thread disorder
  • a) needle in its lower turning point in the last puncture hole,
  • b) needle in its upper reversal point above the penultimate puncture hole,
  • c) needle moving to the upper reversal point after a new puncture into the penultimate puncture hole,
  • d) needle in its upper turning point above the penultimate puncture hole after the new puncture,
  • e) Seam formation continues.

In a sewing machine (1) with housing parts (2) indicated in FIG. 1, an arm shaft (3) is mounted, which carries a pulse disk (4) of a pulse generator (5). A wider marking (6) and a narrower marking (7) are formed offset from one another on the pulse disk (4). The markings (6, 7) can be monitored by a sensor device (8) of the pulse generator (5).

One end of the crank (10) is articulated eccentrically on a disc (9) formed in one piece with the arm shaft (3), the opposite end of which engages via a clamp (11) on a needle bar (12) which carries a needle (13) .

For the transport of a sewing material arranged on a base plate (14) (FIG. 4), the sewing machine (1) has a fabric pusher (15) which protrudes through slots in a needle plate (16) (FIG. 4) accommodated by the base plate (14) . The fabric pusher (15) is carried by a fabric pusher carrier (17) (FIG. 1), the fork-shaped end of which engages around an eccentric (19) attached to a shaft (18), the shaft (18) passing the fabric pusher (15) per stitch formation cycle issued a lifting movement. The free end of the The fabric pusher carrier (17) pivots on a pin of a rocker (20). The rocker (20) is fork-shaped with arms and is arranged in a rotationally fixed manner on a shaft (21) which gives the fabric pusher (15) a feed movement per stitch formation cycle.

On a hook drive shaft (22), which is driven in a ratio of 2: 1 to the arm shaft (3) or to a stitch regulator drive shaft (23), a double lockstitch hook (24) is attached just below the fabric slide (15). A thread monitor (25) and a cutting device (26) are assigned to the gripper (24).

The elements required for the function of the thread monitor (25) are shown enlarged in FIGS. 2 and 3. The bobbin case (27) of the hook (24) is provided with an annular wall in which an outlet opening (28) for the hook thread of a bobbin (29) is formed. The ends of a groove (30) which forms a guide surface and is provided on at least part of the circumference of the bobbin case (27) adjoin the outlet opening (28). A deflection surface (31) for light rays is recessed in the wall of the bobbin case (27). The deflection surface (31) is provided behind the outlet opening (28) in the thread withdrawal direction and is monitored by a photodiode (32) and a photodetector (33) of the thread monitor (25) designed as a phototransitor. The deflection surface (31) is inclined relative to the photodetector (33) in the wall of the bobbin case (27), on the outside of which a spring (34) is fastened for tensioning the looper thread.

The cutting device (26) of the sewing machine (1) is in Fig. 4 shown enlarged. The thread catcher (35) of the cutting device (26) provided for gripping the hook thread is arranged coaxially with the hook (24) and interacts with a cutting knife (36), indicated by dash-dotted lines, on the underside of the base plate (14). The thread catcher (35) is fastened to a support arm (37) which is connected to a ring (38) which loosely surrounds the hook drive shaft (22). This is secured in the axial direction and rotatably mounted in a ring element (39) which is attached below the base plate (14). A link (40) is articulated on the support arm (37) and is connected to an arm of an angle lever (41) which is supported by a bearing block (42) fixed to the housing. The other arm of the angle lever (41) is connected via a link (43) to the piston rod of a pneumatic cylinder (44) designed as a pressure intensifier.

On the stitch regulator drive shaft (23) (Fig. 1), two eccentrics (45, 46) are arranged in a rotationally fixed manner. An eccentric rod (47) encompassing the eccentric (45) is connected at its opposite end in an articulated manner to a rocker (48) fastened to the shaft (18). A second eccentric rod (49) encompassing the eccentric (46) is articulated on a pin (50) on which a link (51) is mounted, which is supported by means of a pin (52) with a crank attached to the shaft (21) (53) is connected. In addition to the eccentric rod (49), a link (54) engages on the pin (50) and engages around a pin (56) carried by a crank (55). The effective length of the handlebar (51) is equal to the effective length of the handlebar (54), so that when the two pins (52 and 56) are aligned, the shaft (21) in spite of the moving eccentric rod (49) at rest remains.

In order to vary the movement of the eccentric rod (49) acting on the shaft (21), the crank (55) is clamped on an adjusting shaft (57). The adjusting shaft (57) carries a two-armed crank (58), on one arm of which a tension spring (59) attached to the housing of the sewing machine (1) engages. The other arm of the crank (58) rests on a pneumatic two-position cylinder (60) which has two piston rods (61 and 62) and a cylinder jacket (63) divided into two chambers for receiving the piston rods (61 and 62). The piston rod (61) is attached to a housing part (2), while the piston rod (62) rests on the underside of the arm of the crank (58).

The crank (58) is connected via a pull rod (64) to one end of a rocking lever (65) which is fastened on a shaft (66) which is mounted in the housing and carries a shift lever (67). The still free end of the rocker arm (65) has a spherical projection (68) which projects between the side walls of an adjusting groove (69) of an adjusting wheel (70) which is rotatably arranged on an axis fixed to the housing. The elements (50 to 70) form a stitch regulator (71), the stitch length being set in a known manner by turning the setting wheel (70).

The sewing machine (1) is provided with a control device (72), which is shown in simplified form in FIG. 5.

The thread monitor (25) has a regulated voltage source, the positive pole of which has current through the photodiode (32) and a resistor (73) to ground flows. Current also flows from the positive pole of the voltage source via the phototransistor (33) and a resistor (74) to ground. The emitter of the phototransistor (33) is connected via a negation element (75) to an input (E 1) of a microcomputer (76).

The sensor device (8) of the pulse generator (5) is connected to the input (ZE 1) of a counter (77). This has two outputs (ZA 1 and ZA 2), of which the output (ZA 1) is connected to an input (E 2) and the output (ZA 2) to an input (E 3) of the microcomputer (76). An input (ZE 2) of the counter (77) can be reset to zero via a line connected to an output (A 1) of the microcomputer (76).

The microcomputer (76) has an input (E 4) which can be controlled via a foot pedal (not shown) of the sewing machine (1).

Four further outputs (A2 to A5) of the microcomputer (76) are connected to the pressure switching magnets of two 4/2-way valves (78 and 79) via four amplifiers (not shown) and four lines. The directional control valves (78 and 79) are used for the controlled actuation of the two-position cylinder (60) and are supplied by a compressed air source (80). An output (A6) of the microcomputer (76) is connected via an amplifier and a line (not shown) to the pressure switching magnet of a 3/2-way valve (81) which is connected to the compressed air source (80) via a throttle (82). An output of the cylinder (44) controlled by the 3/2-way valve (81) is connected to an adjustable throttle (83).

The outputs (A7 to A11) of the microcomputer (76) are connected via lines to a known control circuit, not shown, of a positioning motor (84) which is in drive connection with the arm shaft (3) via a belt drive (85).

The arrangement works as follows:
After it emerges from the bobbin case (27), the looper thread is guided in at least one thread turn on its circumference in the groove (30). The looper thread covers part of the deflecting surface (31).

The light rays of the photodiode (32) strike the looper thread and, in the case of a larger deflecting surface (31), the exposed parts thereof on both sides of the looper thread. Due to the inclination of the deflecting surface (31) relative to the photodetector (33), the light beams striking the deflecting surface (31) are reflected in a direction in which they cannot be received by the photodetector (33). A part of the scattered light rays reflected on the looper thread, however, reaches the photodetector (33).

The scattered rays cause the photodetector (33) to conduct and current flows through the resistor (74) to ground. The voltage thus applied to the emitter is passed on to the negation element (75), at whose output there is no voltage as long as the photodetector (33) is conductive. If, on the other hand, the looper thread is broken or used up so far that the deflection surface (31) is exposed, no more light rays enter the photodetector (33). While there is no signal at the input of the Negation element (75) is present, a signal is output at its output and fed to the input (E1) of the microcomputer (76).

The signal from the thread monitor (25) causes the microcomputer (76) to emit a signal at its output (A7), by means of which the operating speed of the positioning motor (84) is reduced to a significantly lower speed. At the same time, the microcomputer (76) receives at its inputs (E2 and E3) the signals emitted by the counter (77) of the pulse generator (5).

The counter (77) is put into operation by the entry of one of the markings (6, 7) into the monitoring area of the sensor device (8) and receives a signal at its input (ZE1) until the marking (6, 7) Has left the monitoring area again. As long as the signal is present at the input (ZE1), the counter (77) counts upwards from the value zero, the marking (6), which indicates the lower reversal point of the needle bar (12), being assigned a higher value than because of its greater width the mark (7) which indicates the upper turning point of the needle bar (12). When the higher value is reached, the counter (77) outputs a signal to the microcomputer (76) at its output (ZA1), whereas the lower value outputs a signal at its output (ZA2). After each signal arriving at the inputs (E2 or E3) of the microcomputer (76), the latter outputs a signal at its output (A1), whereby the counter (77) is reset to zero.

When the signal from the counter (77) is present for the first time at the input (E2) of the microcomputer (76), this indicates a signal from its output (A8), whereby the needle (13) is stopped at its lower reversal point in the last puncture hole of the sewing material (FIG. 6a). When the needle (13) is at a standstill, the microcomputer (76) emits signals at the outputs (A2 and A4) which, by reversing the 4/2-way valves (78 and 79), raise the cylinder jacket (63) relative to the piston rod (61 ) and extend the piston rod (62). The free end of the piston rod (62) is thereby moved from position (a) shown in FIG. 5 to position (c). As a result, the two-position cylinder (60) pivots the crank (58) according to FIG. 71) is set to reverse stitch.

After a reverse transport stroke, a signal reaches the output (ZA2) of the counter (77) at the input (E3) of the microcomputer (76). The needle (13) is then in its upper reversal point above the penultimate puncture hole of the material (Fig. 6b). To stop the needle (13) in this position, the microcomputer (76) outputs a signal to the positioning motor (84) at its output (A9).

In this position of the needle (13), new thread of the looper is withdrawn from the bobbin (29) when the thread breaks; at the end of the thread, the empty bobbin (29) is replaced by a full one. After actuating the foot pedal of the sewing machine (1), a signal reaches the input (E4) of the microcomputer (76), whereupon the latter outputs a signal at its output (A3) for reversing the 4/2-way valve (78), so that the cylinder jacket (63) retracts. The free end of the piston rod (62) then takes the Position (b) in Fig. 5, in which the stitch regulator (71) is set to zero. In position (b) the extension (68) of the rocking lever (65) is in a position between the inner and the outer side wall of the adjusting groove (69).

As soon as the stitch regulator (71) is set to zero, a stitch is formed after a signal is emitted at the output (A10) of the microcomputer (76). After the needle (13) has returned to its upper reversal point, this process can be repeated several times for a particularly tight knot. Fig. 6c shows the needle (13) on its way to the upper turning point.

After completing this knotting in the upper turning point of the needle (13), the 3/2-way valve (81) is reversed by emitting a signal at the output (A6) of the microcomputer (76), so that the piston rod of the cylinder (44) extends and the cutting knife (36) drives to cut the two free ends of the looper threads (Fig. 6d). The throttle (82) is effective to delay the time to switch back the 3/2-way valve (81) and the throttle (83) to reduce the piston speed when the piston is retracted.

After thread cutting, the microcomputer (76) outputs a signal to the 4/2-way valve ((79) at its output (A5), causing the piston rod (62) to retract and its free end to position (a) (Fig. 5 The stitch adjuster (71) is thus set again to the forward stitch, and the positioning motor (84) is then accelerated to the working speed again by outputting a signal at the output (A11) of the microcomputer (76) and the seam formation continued.

Claims (2)

1. Method of producing a seam which is continuous at its side facing towards the needle of a sewing machine, and whereby, in the event of a fault at the pickup thread during the production, the operation of the sewing machine is stopped and a new pickup thread is delivered, characterised in that, once a fault has occurred, an initiated stitch-pattern cycle is completed, the sewing machine (1) is stopped with the needle in its bottom position, the stitch platen (71) is set for reverse stitching, the sewing machine (1) is set with the needle in a top position, the stitch platen (71) is set to Zero, and after clearing the fault, at least one stich formation is formed for knotting the new pickup thread to the needle thread in the stitch hole of the needle (13) prior to the occurrence of the fault, and that the production of the seam is continued with the original stitch length.
2. Method according to claim 1, characterised in that, after knotting the new pickup thread to the needle thread, the free ends of the old and the new pickup thread are cut off.

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