US3424116A - Thread cutoff device for lockstitch sewing machines - Google Patents

Description

Jan. 28, 1969 WOLF-RUDIGER VON HAGEN 3,424,116

THREAD CUTQFF DEVICE FOR LOCKSTITCH SEWING MACHINES I Fi'led Aug. 24, 1966 Sheet of 4 INVENTOR WOL'F- RUDIGER VON HAGEM BY mm,

AITTORNEYS Jan. 28, 1969 WOLF-RUDIGER VON HAGEN 3,

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Sheet 2 of 4 Filed Aug. 24, 1966 INVENTOR WOLF- RUDJGER VON HAGEN Jan. 28, 1969 WOLF-RUDIGER VON HAGEN 3,424,116

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Filed Aug. 24, 1966 1 .Sheet' 3 0f 4 INVENTOR WOLl-- RUDIGER VON HAGEN ATTORNEY 5 BY flhwm, @1 wag Ma Jan. 28, 1969 WOLF-RUDIGEF VON HAGEN 3,

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Filed Aug. 24, 1966 Sheet 4 Of 4 WOLF-RUDIGER VON HAGEN IGZ Q W yum/MW ATTOIQNEYS United States Patent 3,424,116 THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Wolf-Rudiger von Hagen, Grotzingen, kreis Nurtingen, Germany, assignor to Union Special Maschinenfabrik, G.m.b.H., Stuttgart, Wurttemberg, Germany Filed Aug. 24, 1966, Ser. No. 574,647 Claims priority, application Germany, Aug. 25, 1965, U 11,982 VIIa 52a; July 15, 1966, U 12,900 VIIa 52a US. Cl. 112252 21 Claims Int. Cl. D05!) 65/02 ABSTRACT OF THE DISCLOSURE -A thread severing device employable in lockstitch sewing machines is disclosed herein and includes a stationary thread cutter and a swingably mounted thread catcher for engaging the needle thread loop and the bobbin thread and moving these threads into cutting engagement with the cutter. The thread catcher is swingably mounted for movement into the needle path at the time the needle thread loop is drawn to its maximum size by a needle thread loop taker normally provided in lockstitch sewing machines. The thread catcher remains in a position proximate the loop taker until the loop taker discards the needle thread loop whereupon the needle thread loop engages the thread catcher and the thread catcher returns to its initial position drawing the engaged threads into cutting operation with the cutter.

The invention concerns a cutoff device for the threads of a lockstitch sewing machine having a stationary knife and a thread catcher movable between the throat plate and the looptaker.

In known cutolf devices for the threads of lockstitch sewing machines in which both threads are cut off underneath the throat plate, a thread catcher moves into the needle thread loop during the last revolution of the machine, catches a limb of the same as well as the bobbin thread and draws both out a predetermined amount before the threads are cut. The movement of the thread catcher is controlled by the sewing machine, usually by means of a cam plate, in such a manner that the thread catcher at a specific moment enters the needle thread loop and subsequently draws out the threads, which are then cut off before the sewing machine is stopped.

These cutoff devices require an extremely accurate course of the movement of the thread catcher synchronously with the stitch formation, said course of movement requiring a complicated and expensive drive which includes a control device. In addition, this cutoif device or, more particularly the thread catcher, requires a relatively large space between the throat plate and the loop taker, wherefore such cutoff devices, as a rule cannot be used on sewing machines wherein the loop taker is disposed directly below the throat plate in order to obtain an arrangement which is most favorable for the forming of the stitches.

The invention serves the purpose of providing means associated with lockstitch machines for cutting of the threads under the throat plate, and it contemplates solution of the technical problem of creating a cutoff device whose course of movement is simple to control, which needs little space, and, above all, which also can be installed in existing machines having the looptaker arranged at a small distance beneath the throat plate.

This problem is essentially solved by timing the movement of the thread catcher which is directed into the path of the needle above the bobbin case restraining finger, in such manner that the thread catcher moves into the needle path at the time when the needle thread loop is "ice drawn out to its maximum size, and that it remains in this position until the needle thread loop after being cast 011? from the looptaker has deposited and drawn itself around the thread catcher and that thereafter it moves back against the stationary knife.

This course of movement of the thread catcher does not require any expensive mechanism, because it is only necessary to place' the thread catcher into catching position at a predetermined moment of the sewing cycle and to release it again from that position at another moment, whereupon it is retracted to its starting position in a known manner by the force of a spring. In this position the threads are then cut off. From the fact that the thread catcher does not actually move into the needle thread loop, but rather the latter is formed around the momentarily stationary thread catcher, it follows that a relatively large tolerance is allowed for the timing of the swinging movement in inwardly and outwardly directions. Thus the movement imparting and control means may be of a relatively simple construction. The thread catcher is preferably actuated by a solenoid which is controlled by a contact bridge, for example, olf the synchonizer of a needle positioning motor.

A further essential characteristic consists in the fact that the thread catcher cooperates within reach of the knife, with a clamping surface for clamping the end of the thread going to the needle and also that to the bobbin. The provision of a clamping surface disposed for cooperating with the thread catcher eliminates the need for a special pulling out of the threads. The cutoff device can be arranged in the immediate vicinity of the loop taker. The clamping of the threads prevents the unthreading of the needle and insures a certain sewing start. In addition, through the clamping of the threads and arrangement of the cutoff device near the loop taker, the severed thread ends projecting from the material are kept short, both at the beginning and at the end of the seam.

The thread catcher is preferably mounted swingably on the support of the bobbin case restraining finger. This support of the bobbin case restraining finger also suitably carries the stationary knife and forms a guiding surface which cooperates with the thread catcher for clamping the ends of the threads going to the bobbin as well as to the needle. By virtue of this arrangement of the thread catcher and the construction of the support for the bobbin case restraining finger, said support being adapted to accommodate the stationary knife and form a guiding and clamping surface, the cutting device becomes particularly simple as it does not require a support of its own and may most advantageously be incorporated into existing machines.

The plane of movement of the thread catcher extends suitably through the path of the thread seizing beak on the hook assembly. The arrangement of the plane of movement intersecting or passing through the path of the thread seizing beak is possible due to the course of the movement of the thread catcher in accordance with the invention, because, during the time when the thread catcher is swung into its loop intercepting or catching position, the thread seizing beak is outside the path of movement of the thread catcher. As a result of this, the loop taker may be arranged, as usual, in close proximity to the underside of the throat plate or the underside of the feed dog, said arrangement being particularly advantageous for the stitch formation especially in high speed sewing machines.

In another form of the invention, a clearance recess or channel is provided between the running-on or guiding surface of the bobbin case-retainer finger and the thread catcher for the reception and the unimpeded passage of the thread strands or portions drawn out by the thread catcher and running to the bobbin and to the needle.

Through this development of the cutting off device, the threads, after being cut off, will lie in a clearance or channel which is covered by the overlying swung-in thread catcher and said thread portions are kept in the desired position. However, the channel is wide enough so that the thread portions can be pulled out from the channel without any objectionable resistance. As a result, the desired end of evenly pulling off the threads at the start of sewing will be achieved, independently of the thickness of the thread, and the beginning of the seam with an even appearance will be accomplished.

In order that the cutting off of ends of the thread at the end of the seam will be kept short, and that sufficient thread be made available at the start of sewing, thus to guarantee a safe formation of the first stitch, the thread catcher is provided with a cutting edge protruding in the direction of the cutting knife and which trails the edge of the thread catcher serving to catch and draw out the thread. Through this development of the thread catcher, the separation or severing of the threads takes place close to the stitching hole of the needle plate, and as a result the ends of the thread at the end of the seam are kept short. By reason of this arrangement of the edge of the thread catcher which seizes and draws out the thread a distance ahead of the cutting edge which is presented for cooperation with the cutting knife, the ends of the thread running to tthe bobbin and to the needle will obtain a sufficient length, so that without jammig the ends of the thread, a safe formation of the first stitch will be assured at the start of sewing.

For the purpose af guiding the threads safely into the channel, the thread catcher has been equipped with guiding edges, serving to hold the threads in a predetermined position as they are being presented to said channel.

In order to assure that the threads will properly engage against the guiding edges, a novel arrangement of guiding element has been provided which directs the loop of the needle thread which has been drawn around the bobbin case and which has been released by the gripper point, to the guiding edges of the thread catcher. This guide element, according to one design, consists of a spring part attached to a swinging part of the thread catcher, preferably a spring wire which will resiliently engage against the carrier of the bobbin case when the thread catcher has been swung out. This guiding element will, particularly in the case of strongly twisted threads, prevent the loop of the needle thread which breaks away from the gripper point from being drawn around the gripper tail, so that said thread will follow around the guide element and be held by the latter until it is drawn away through taking-off of the thread. In this way, the strands of the needle thread are directed securely against the guiding edges of the swung-out thread catcher.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a fragmentary vertical cross sectional view taken through the bed and throat plate of a lockstitch machine having embodied therein a cutoff device arranged according to the invention.

FIGURE 2 is a plan view illustrating the cutoff device shown in FIGURE 1.

FIGURE 3 is a perspective view depicting the thread catcher immediately after the swinging inwardly.

FIGURE 4 is a view similar to FIGURE 3 and showing the needle thread loop intercepted by the thread catcher before the thread catcher swings back.

FIGURE 5 is a perspective view of the cutoff device shown in FIGURE 3 but with the thread catcher in the starting position.

FIGURE 6 is a diagram schematically showing the course of movement of the needle, the loop taker and the thread catcher during the last revolution of the main shaft of the sewing machine.

FIGURE 7 is an exploded perspective view illustrating a modified form of cutoff device embodying the invention.

FIGURE 8 is a perspective view illustrating the cutoff device of FIGURE 7 with the thread catcher in its swung-out, needle thread intercepting or receiving position.

FIGURE 9 is a view like FIGURE 8 but with the thread catcher swung in, or back to its starting position.

In the practical development of the invention as shown in FIGURES 1 through 6 the support 3 of a bobbin case restraining finger 4 is fastened in the usual way on the bed 1 of a lockstitch sewing machine, which bed carries a throat plate 2, said throat plate 2 having needle hole 5 for passage of the needle 6. In addition, a conventional double rotating lockstitch loop taker 7 is shown, the same being driven by the shaft 8.

According to the present invention, a thread catcher 9 is swingably mounted on the support 3 for the bobbin case restraining finger 4. The thread catcher 9 consists preferably of a thin plate fastened on a swing arm 11. A projection 10 on the swing arm 11 abuts in the starting position, limiting the movement of said arm. The swing arm 11 is mounted on a rock shaft 12 extending through and journalled in said support 3 for the bobbin case restraining finger 4. Said rock shaft 12 carries at its other end an actuating lever '13, which is coupled to a solenoid (not shown). In addition, there is received on the rock shaft 12 a return spring 14, whose one end 15 engages said actuating lever 13 and whose other end 16 abuts a stop pin 17 fastened to said support 3. The return spring 14 is retained on the rock shaft 12 by a retaining ring 18, as best shown in FIGURE 1.

A knife 19 is screw-secured onto the support 3. The actual knife edge 21 is disposed some distance above a guiding surface 22 of support 3. If retracted to its starting position, shown in FIGURE 2, the thread catcher 9 is guided along said guide surface 22 and enters the open gap between the guide surface 22 and the knife 19. The knife 19 preferably consists of a resilient steel plate. The side of the thread catcher 9 that is turned toward the knife 19 is shaped in such fashion that it enters the gap between the knife 19 and the guiding surface 22 like a wedge, displacing said resilient knife 19 upward.

In FIGURE 3 the needle thread loop is shown as being drawn out to its maximum size. This position corresponds approximately to the positions according to FIG- URES 1 and 2. At this particular time the thread catcher 9 swings into the position illustrated, namely, into the region of the path of the needle or the loop forming area, whereby the needle thread limb going to the last stitch, and the bobbin thread 26 are placed automatically on that side of the thread catcher that is turned towards the knife. The limb 27 of the needle thread loop going to the needle is placed on the opposite side. The thread catcher 9 remains in this position until the needle has reached about its highest position, which corresponds approximately to a position of the loop taker 7 as shown in FIGURE 4. Between the two positions shown in FIG- URES 3 and 4, the loop taker 7 has carried the needle thread loop around the bobbin and the loop has, through the take-up of the needle thread, disposed itself around the thread catcher 9.

The thread catcher 9 now swings back into the starting position as shown in FIGURE 5, where it cuts the threads and clamps the bobbin thread 26 and the strand 27 of the needle thread loop extending to the needle. This clamping of the threads is of particular importance. The clamped in bobbin thread insures a certain start of the next sewing operation, and in addition, a relatively short bobbin thread end at the beginning of the seam. The clamping of the needle thread prevents unthreading of the needle, because the needle thread is pulled through the thread take-up approximately at the time of the cutting operation. The needle thread is held to such length that a sure stitch formation Will result when the sewing operation is resumed and that the projecting end at the beginning of the seam corresponds in length approximately to the projecting end of the bobbin thread.

The tension of the needle thread is preferably released during the swinging back of the thread catcher, so that the thread take-up does not draw the needle thread out of the clamp. After the needle thread take-up has reached its terminal position, the thread tension is again applied so the needle thread is not drawn from the spool when the material is being removed, but merely the end of the needle thread out of the clamp.

FIGURE 6 is a schematic illustration of the course of the movement of the needle, the loop taker and the thread catcher during the last revolution of the main shaft of the machine. The movement curve of needle a and loop taker b commence at the highest position of the needle. The thread catcher 9 swings into the path of the needle at A about 100 (this meaning 100 of the angular movement of the main shaft) before reaching the terminal position of the needle (high position of needle), and remains in this position over the distance A-B to swing back again to the starting position immediately before reaching the terminal position at B.

In the form of the invention illustrated in FIGURES 7 to 9, there is again a thread catcher 9a swingably mounted on the support or carrier 3a of a bobbin case restraining finger 40. As in the previously described form, the thread catcher 9a is attached by screw means 30 to a swinging arm 11a, disposed to have its projection a rest against the carrier 3a when in the starting position, comparable to the illustration in FIGURE 2. The arm '11a is swingably mounted in the carrier 3a by means of a rock shaft 12a. Also, a knife 19a is screw secured at 31 onto the carrier 3a, said knife having cutting edge 21a.

In this form of the invention, however, a clearance recess or channel 32 is provided in the running-0n or top guiding surface 2201 of the bobbin case restraining finger 4a, the thread catcher 9a being disposed in position for swinging across said channel. The thread catcher 9a has a cutting edge 33 protruding in the direction of the knife 19a and its edge 21a, said edge 33 being offset from or trailing the edge 34 of the thread catcher 9: as clearly shown in FIGURE 7.

During the drawing out of the threads, the edge 34 serves in seizing and drawing out the threads. Additionally, the thread catcher 9a is provided with guide edges 35, 36, as clearly shown in FIGURE 7. A spring wire 37 is attached with one end in the swinging arm 11a and it engages resiliently with the carrier of the bobbin case whenever the thread catcher 9a has been swung out, as shown in FIGURE 8.

It is to be understood that when the thread catcher 9a is swung into position for cutting off the threads, the spring wire 37 will engage against the carrier 38 of the bobbin case, and the needle thread, which had been drawn out from the needle 6a by the seizing beak of the loop taker 39 into a loop running around the bobbin case, will be engaged by the spring wire 37 after release by the gripper point 39, as shown in FIGURE 8, as a result of which any looping of said needle thread around the gripper tail 40 will be prevented. The spring wire 37 will hold the loop of the needle thread firmly as shown in FIGURE 8, until it is drawn off through the taking-off of the needle thread. As a result, the strand or portion 41 of the loop of the needle thread running to the needle, will be directed to the guiding edge 36 and the strand or portion 42 of the thread running to the last stitch will be directed to the guiding edge 35 as will be apparent by reference to FIGURE 8, and in this position will loop around the thread catcher 911.

When the thread catcher 9a now swings back into its starting position, it will draw the strand or needle thread portion 41 of the thread running to the needle into the clearance or channel 32 of the bobbin case restrainer finger 4a, into which channel the thread strand 4'3 running into the bobbin and seized by the guiding edge 35 is likewise drawn. The projecting cutting edge 33 of the thread catcher 9a will run against the fixed cutting knife edge 21a and will sever or separate the threads. The strands or portions 41 and 43 of the needle thread are held freely in the channel 32 after separation of the threads and can be drawn off without resistance.

While preferred forms of the invention have been disclosed in detail herein, it is to be understood that variations in part structure and arrangement may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a lockstitch sewing machine wherein are included stitch forming means including an uprightly reciprocable needle, a throat plate, a seizing beak equipped loop taker and shaft disposed closely beneath the throat plate and a bobbin case, the combination of thread severing means disposed closely adjacent said plate and loop taker, a bobbin case restraining finger projecting into proximity with said bobbin case for maintaining the position of said bobbin case, a restraining finger support mounting said bobbin case restraining finger and including a portion traversing and arched over the axis of said shaft and adjacent the loop taker and bobbin case, said thread severing means comprising a stationary knife mounted on said support, and thread catcher means swingably mounted on said support for moving above said restraining finger into the needle path when a needle thread loop has been drawn out to its maximum size for remaining in said path to catch the needle thread loop upon the casting off of the needle thread loop by said loop taker and for moving back toward the knife to cooperate therewith in a thread severing action.

2. The combination defined in claim 1 wherein the restraining finger presents a surface engaged in guiding and thread clamping contact with the thread catcher means.

3. The combination defined in claim 1 wherein the restraining finger presents a surface engaged in guiding and thread clamping contact with the thread catcher means, and wherein the stationary knife is resilient and spaced above the support, said thread catcher means being movable into wedging engagement between said support and knife.

4. The combination defined in claim 1 wherein the restraining finger presents a surface in guidingcontact with the thread catcher means, said surface being recessed to receive threads Without clamping action.

5. The combination defined in claim 1 wherein the thread catcher means includes independent spaced guide edges each disposed for engaging and holding threads in a predetermined position.

6. The combination defined in claim 1 wherein the restraining finger presents a surface engaged in guiding contact with the thread catcher, the knife being resilient and bearing such spaced relation above the support that the thread catcher engages in wedging action between the support and knife, the thread catcher having thereon a lead-in edge portion for first entering the space and a spaced trailing cutter edge portion disposed to thereafter enter the space and engage in thread cutting contact with the knife.

7. The combination defined in claim 1 wherein there is included a spring element carried by the thread catcher swing mounting and having a free end overlying and engageable with the bobbin case carrier for yieldably holding a thread loop thereagainst.

8. A thread cutoff device for severing threads in a lockstitch sewing machine of the type including a reciproca-ble needle, a throat plate mounted for cooperation with said needle, a bobbin case, bobbin case restraining means and loop taker means for passing the needle thread loop around said bobbin case, said cutoff device comprising thread cutting means mounted proximate said loop taker, thread catcher means for catching the needle thread loop upon release thereof from said loop taker means, said thread catcher means being mounted for movement above said bobbin case restraining means, means for moving said thread catcher means into the path of said needle when said loop taker means draws the needle thread loop to its maximum size and for returning said thread catcher means from the path of said needle and into thread cutting cooperation with said thread cutting means, said bobbin case restraining means further comprising a bobbin case restraining finger and support means mounting said bobbin case restraining finger, said thread catcher means being swingably mounted upon said support means for swinging movement into the path of said needle and for return swinging movement away from the path of said needle.

9. A thread cutofi device according to claim 8- wherein said cutting means comprises a stationary knife mounted upon said support means for thread severing cooperation with said thread catcher upon the return of said thread catcher from the path of said needle.

.10. The cutofl? device according to claim 9 wherein said thread catching means includes a thread engaging and moving edge and a thread cutting edge projecting toward said cutting knife, said thread engaging and drawing edge projecting beyond said cutting edge toward said cutting knife to provide thread cutting after said thread engaging and drawing edge has moved past said cutting knife.

11. A cutoff device according to claim 9' wherein said support means have formed thereon thread catcher guiding surface means closely adjacent the path of movement of said thread catcher means for clamping severed threads against said thread catcher means.

12. A thread cutolf device according to claim 11, said loop taker means including a thread seizing beak movable into engagement with the needle thread loop for passing the loop around a bobbin, said thread catcher means being mounted for movement in a plane of movement passing through the path of movement of said thread seizing beak.

13. The thread cutofi? device according to claim 9, said support means including thread catcher guiding surface means adjacent a portion of the path of movement of said thread catcher, said guiding surface means having a channel formed therein for the reception of portions of severed threads to prevent clamping of the received thread portions between said thread catcher means and said guiding surface means.

14. The thread cutoff device according to claim 13 wherein said guiding surface means and said channel are provided upon said bobbin case restraining finger.

;15. In a sewing machine of the type including a throat plate, bobbin support means for mounting a bobbin beneath the throat plate and needle thread loop taking means for passing a needle thread loop around a bobbin supported by said bobbin support means, the combination comprising thread cutting means for engaging and severing the needle thread in the loop thereof and thread catching means normally disposed adjacent said cutting means and spaced from said loop taking means and movable for engaging the needle thread loop and moving the portion of the loop to be severed into engagement with said cutting means, said thread catching means comprising swingably mounted thread engaging arm means swingable from an initial position thereof to a second position proximate said loop taker for receiving the needle thread loop from said loop taker while in said second position and retractable from said second position to said initial position for carrying the portion of the needle thread loop to be severed into severing engagement with said cutting means.

16. The combination according to claim 15 wherein said thread catching means further comprises movement imparting means mechanically connected to said thread engaging arm means for moving said thread engaging arm means to the second position thereof proximate the loop taker, for maintaining said arm means in said second position until release of the needle thread by said loop taker and for returning said arm means to said initial position following release of the needle thread by said loop taker.

17. A thread cutoll device according to claim 15 further comprising clamping surface means adjacent said thread cutting means for clamping a needle thread and a bobbin thread upon movement of the threads into cutting engagement with said thread cutting means by said thread catcher means.

18. The cutoff device according to claim 15, said loop taking means including a thread seizing beak movable into engagement with the needle thread loop for passing the loop around a bobbin, said thread catching means being mounted for movement in a plane of movement passing through the path of movement of said thread seizing beak.

19. The cutoff device according to claim 15 wherein said thread catching means includes guide edge means for engaging and holding threads in a predetermined position for the severing thereof.

20. A thread cutoli device according to claim 19 further comprising needle thread guide means for guiding the needle thread loop into engagement with said thread catcher means upon release of the needle thread loop by said loop taker means.

21. A thread cutoff device according to claim 20 wherein said needle thread guide means comprises a resilient spring element attached to and movable with said thread catcher means for movement into resilient engagement with a portion of said bobbin case restraining means for clamping the needle thread against said portion of said bobbin case restraining means during positioning of the needle thread in engagement with said thread catcher means.

References Cited UNITED STATES PATENTS 1,319,668 10/1919 Morris 112-252 1,346,814 7/1920 Pifield 1l2252 1,401,973 1/1922 Fifield 1l2252 1,228,871 6/1917 Barron ll2252 1,395,274 11/1921 Hagelstein 112252 3,173,392 3/1965 Hedegaard 1l2-252 3,173,393 3/1965 Adam 112252 HERBERT F. ROSS, Primary Examiner.

Images