US3888198A - Thread cutter device on chain stitch sewing machine - Google Patents

Abstract

The disclosure relates to an automatic cutting means which is attached to the looper means of a chain stitch sewing machine in such a way that the recoil involved in stopping the machine at the end of a predetermined group of sewing stitches operates to cut that leg of the thread loop which is adjacent to the goods just sewed.

Description

United States Patent 1 1 Bauer et a1.

1 1 THREAD CUTTER DEVICE ON CHAIN STITCH SEWING MACHINE [75] Inventors: Wilhelm Bauer, Hauptstuhl; Horst Stahlschmitt, Kaisers Lautern. both of Germany [73] Assignee: Pfaff Industriemaschinen GmbH,

Kaiserslautern. Germany [22] Filed: May I6, 1974 [211 App]. No: 470,543

[30] Foreign Application Priority Data May 19, 1973 Germany 2325564 [52] U.S. Cl 112/252; 112/197 [51] Int. Cl D05b 65/02 [58] Field of Search 112/252, 197, 198, 201,

1 1 June 10, 1975 [56] References Cited UNITED STATES PATENTS 2.163.994 6/1939 Fischer 112/252 2.345943 4/1944 McCann 112/252 $051,111 8/1962 Cortcse et a1 112/252 Primary Examiner-H. Hampton Hunter Attorney, Agent. or Firm-Frank L. Durr; Orville N.

Greene [57] ABSTRACT The disclosure relates to an automatic cutting means which is attached to the looper means of a chain stitch sewing machine in such a way that the recoil involved in stopping the machine at the end of a predetermined group of sewing stitches operates to cut that leg of the thread loop which is adjacent to the goods just sewed.

3 Claims, 6 Drawing Figures ageaalsaa PATENTEDJUH 10 I975 SHEET I THREAD CUTTER DEVICE ON CHAIN STITCH SEWING MALIIINE The invention concerns a thread-cutting device on a chain stitch sewing machine of the ty pe having a stop ping arrangement for stopping the main shaft in a predetermined angular position. a rotating looper with a looper point and also a looper back and with it the needle threadJoo severing cutting blade.

It is known. in connection with single thread chain stitch sewing machines. to sever the thread loop above the looper upon stopping the main shaft of the machine and lifting the sewing goods or the sewing goods clamp. Since a uniform thread. as a rule. tears off in the area of a knot. there results. from this method, that the initial length of the thread end on the supply side is predestined to be proportionately short. The latter kind of thread severing can be carried out only with thread of inferior strength and on correspondingly stout sewing goods.

It has. to be sure. already been made also. thread loop arrangements for single thread chain stitch sewing machines by which a cutting knife for the thread is fastened directly to the auxillary looper. There. the auxillary looper carrying shaft is axially slidable and is shifted at the end of the sewing process to a supported position in front of the stitch structure. In this position. the cutting knife. fastened on the auxillary looper. comes in the range of the thread loop and severs the latter. Then. the auxiliary looper must execute. in addition to this. a significantly greater oscillating movement in the opposite direction to its normal oscillating movement. requiring an additional operation for attaining a cutting movement. The latter must. after the stopping of the main shaft. be inserted to its predetermined position through the stopping arrangement. and again be disconnected after the ensuing cutting step. Since. in the course of the cutting step. neither the main shaft nor the looper shaft. restored to its original rotating direction. is allowed to be rotated. this drive must take place independently of the drive of the main drive shaft. Such arrangements require. in this way. a comparatively large construction expenditure.

An object of the invention is to provide a thread cutter arrangement for chain stitch sewing machines hav' ing a stopping device wherein the main shaft of the machine is stopped in a predetermined position. which at the end of each stitch forming cycle automatically severs the thread loop. which operates without making an inserted impulse or specific motion necessary.

The problem is solved according to the invention. in that the rotating looper is impelled. after the stopping process through the known recoil movement of the stopping means. to rotate opposite to its loop seizing direction. and the cutting knife is arranged with its cutter extending in the direction of the looper point above and spaced from the looper back.

While with a sewing machine equipped with a stopping arrangement. as for example. stitch-series sewing machines. the main shaft is. first of all. decelerated with the aid of a brake. from its normally operated speed. to a harmless speed for the effective operation of the repel cam. First then. the repel cam engages the arresting slot and will. on account of its spring arrangement. take off around a predetermined angular amount in the working direction of rotation of the main shaft. As soon as the oscillating movement of the machine shaft no longer surpasses the force of the spring. the main shaft rotates back against the working direction of rotation a predetermined angular amount. corresponding to the tension of the spring produced recoil moment. This. by itself undesirable. but unavoidable. recoil of the main shaft. as well as the looper shaft. for attaining the greatest possible reduction in speed or rotation. is taken advantage of for severing the needle thread loop with the cooperation of a knife blade directly fastened to the looper. In this way. a completely automatic cutting process takes place at the end of each stich forming cycle and requires neither a constructive expenditure. nor an increase in the cycle time. Not only the conversion of the cutting tool to its working position. but also the cut ting process itself. takes place in the proper stopping time of the main shaft.

When the new thread cutting device is operated. it is only that leg of the thread loop directly connected to the sewing goods that is severed. so that the remaining leg connecting the thread supply, retains a sufficient length for forming the united stitches of the following sewing cycle. so it is advisable that the cutting knife be so arranged that its cutting edge extends in a concave plane essentially parallel to the plane of the rotating looper. and with said edge facing the point of the looper and turning towards the boundary edge of the back of the looper.

A special construction of the cutting knife. which does not interfere with the normal stitching. according to a further feature of the invention. is that the side thereof which turns away from the looper point is constructed as a lead cam for that leg of the thread loop directed to the sewing goods.

The invention will be further explained in the following description of an embodiment thereof shown in the attached drawings.

In the drawing:

FIG. I is a front view of a chassis-stitch. stitch group sewing machine shown partly in section and with the stopping means in operating position.

FIG. 2 is a partial view of the machine of FIG. 1 with the stopping means in inoperative position.

FIG. 3 is a side view of the stopping means in inoperative position.

FIG. 4 is a side view of the stopping means after the snapping of the knock-off cam.

FIG. 5 is a perspective view, somewhat diagrammatic of the looper with the cutting knife.

FIG. 6 is a perspective view from below of the machine of FIG. 1.

In the front view of FIG. 1. the sewing machine has an arm 1, supported on upright 2. and a lower arm 3. In arm 1. the main drive shaft 4 is mounted to the forward end of which is connected the crank 5. and a link 6 and a needle rod member 7 connects crank 5 to the needle rod 9, containing the needle 8.

The needle rod 9 is slidably received in frame I0 which is pivotally mounted in journal II, which is parallel to the main shaft 4. On its lower end. the frame 10 is pivotally connected through journal I2 to crank 13. which in turn is carried on an oscillating shaft I4, parallel to main shaft 4. The oscillating shaft I4 is connected by means ofa ball pull rod 15 with the arm 16 of a double arm lever I7. in order to attain the lateral movement for the needle rod 9. the lever I7 being pivotally mounted in the bearing block 19. The arm I8 of lever 17 carries. on its free end. a stud 22 engaging in the central groove of control wheel 21. The control wheel 21 is mounted on housing fixed trunnion 23 and is driven by worm gear 24, which meshes with screw gear 25 mounted on the main shaft 4.

The main shaft 4 provides the driving connection for a two-part, trained, vertical shaft 27 through the pair of bevel gears 26. The lower end of shaft 27 is connected through another pair of bevel gears 28, in driving connection with the looper shaft 29, running parallel to the main shaft 4. The two parts of shaft 27 are connected to one another through a known type of crank drive 30, so that the looper shaft 29 develops an irregular speed of movement.

On its forward end, the looper shaft 29, carries the rotating chain stitch looper 31, for cooperating with the needle 8, which in the known way, comprises a loop pick-up point 32, (FIG. 5), as well as an opposed arranged looper back 33.

The looper 31 is provided with a supplemental shoulder 34 for stabilizing of its point-siezed thread loop.

On the shaft-facing surface 35 of looper 31, the cutting knife 36 is fastened, whose cutter 37 is arranged above the looper back. The cutter 37 is essentially parallel to the shaft 29 and is spaced at a fixed distance from back 33. The cutter 37 is concavely curved and, for reasons to be further explained below, is situtated in the background a fixed amount with respect to the boundary surface 39 of the back 33 opposite the looper point 32.

The turned away side of cutter 37 of cutting knife is, as is obvious from FIG. 5, shaped to act as a lead cam for the needle thread loop. The knife 36 adversely affects neither the seizure of the thread loop, nor the for mation of the needle thread triangle in the known way, during the stitch production.

In the embodiment shown in FIGS. 1 and 6, the stitch group machine is a button sewing machine, which in place of the usual feeding means for the sewing goods, shows only the pivotally mounted button clamp. On this basis, an auxilliary looper 40 cooperates in the known way with the rotating chain-stitch looper 31, which is held on shaft 41 parallel to the looper shaft 29. For the driving ofthe auxiliary looper 40 in an oscillating movement, there is provided an eccentric 42 on the shaft 29 which is situated in positively connected driving connections with rocking levers 43 carried on shaft 41.

The main shaft 4 is driven by a stationary motor with a rotating drive (not shown) which transmits its drive through belt 44 to drive pulley 45 fixedly connected to the main shaft 4. Laterally of the drive pulley 45, an idler pully 46 is arranged, which is freely rotatable on the shaft 4, and axially spaced from drive pulley 45.

Within the cup-shaped formed drive pulley 45 are (see FIGS. 3 and 4) two buffer means 47,48 arrnaged, the buffer means 47 being held on the peg 49 fastened to the drive pulley 45, whereas the buffer means 48 is carried on its peg 50 which in turn is held on the rotatably supported pulley 51 (see FIG. I) mounted on a lug of pulley 45.

As especially shown in FIG. 3, there is arranged be' tween the two buffer means 47,48 an arcformed, trained spring 52, which in its relaxed condition holds the buffer means 47 carried by pulley against the opposing segment 53. The pulley 5] is secured against dropping out sideways by means of a cover plate 54 fastened on the front face of the drive pulley 45, and as FIG. 2 shows, is provided with a lifting flank 55, which in the range of its apex, ends in a slot 56 for the knocking-off cam 57. The knocking-off cam 57, at its upper end. is connected with a journal 58 which is pivotally supported on carrier 59.

The carrier 59 is pivotally supported on upright 2 at its lower end with the aid of a bolt 60. On its lower side, the knocking-off cam 57 is forked and is hinged to the leveled off upper region of rod 61 which is pivotally received in the pivotally supported guide 62 of carrier 59.

Between the guide 52 and the adjustable nut 63 at the lower end of rod 61, a spring 64 is provided for a purpose to be described below. The carrier 59 will. by means of its being supported at one end by upright 2 and in the area of its upper end by spring 65, be urged to an operating position, in which the knocking-off cam 57 is engaged in the stop slot 56 of pulley 51. The carrier 59 is provided, at its lower end. with a catch 66 which cooperates with counter-latch 67 to permit run ning of the machine. The counterlatch 67 is arranged at the free end of the a control lever 69 pivotally sup ported on upright 2 by means ofa journal screw 68, the other end of lever 69 cooperating with control cam 70 fastened to control wheel 20. The control lever 59 is held, with the aid of spring 71, in its secured position in which knock-off cam 57 is out of engagement with pulley 51, whereby the counter-latch 67 is prevented from moving in a counterclockwise direction to allow the carrier 59 to pivot on its axis serving bolt 60.

In order to brake the main shaft 4 down to a harmless speed for the knocking-off cam to operate, the face of drive pulley 45 (FIGS. 3-4), serves as the application surface for a segment-like formed brake shoe 72, which is arranged at the upper end of brake lever 74, pivotally supported on carrier 59 in journal 73. The brake lever 74 is urged towards its braking position by means of a spring 75 having one end supported on upright 2, and the other end held by the lever 74.

In order to prevent the brake plate 72 from becoming active during the running of the machine, a journal screw 76 is fastened on carrier 19 which projects through a slot-like clearance 77 for brake lever 74 and thereby limits the movement of the brake lever relative to the carrier 19.

In order to connect the machine, i.e., to transfer the belt 44 from the idler 46 to the drive pulley 45 with the aid of the belt guide 78 fastened on carrier 59, as well as to free the brake plate 72 and the knock-off cam 57, a lever 79 pivotally supported on upright 2, is provided. lts lower end is connected to a pedal actuated tie rod 80 while its upper end operates in the area of catch 66 on carrier 59, and swings the carrier 59 in a clockwise direction against the action of springs 65.75 until the counter link 67 siezes the latch 66 of carrier 59.

The new thread cutting arrangement operates as follows:

During the normal stitching operation. the looper point 32 seizes the needle thread loop and widens it in the known way to form the needle thread triangle. Thereby the shank leading to the thread supply is guided over the looper back and proceeds then to hug the shoulder 34 parallel to the boundary limiting surface 39 facing the point 32 of looper back 33. The shank of the loop leading to the sewing goods slides next over the lead cam 38 of the cutting knife 36 and the thread loop will then be guided over the looper back 33 to snap off of the looper 31.

At the end of the sewing, the severing of the needle thread loop results simultaneously with the stopping of the main shaft 4. To this end, the control cam 70, fas tened on the control wheel 21, temporarily actuates the control lever 69, to thereby turn the same in a counterclockwise direction about journal 68. The catch 66, at the lower end of carrier 59, is thereby set free so that carrier 5). through the operation of spring 65 performs a counter-clockwise swinging movement about bolt 60. The belt 44 is shifted with the aid of belt guide 78 from the drive pulley 45 to the idler pulley 46. Simultaneously therewith, the brake lever 74, through operation of its spring 75, is pivoted about is journal 73. The brake plate 72 contacts the face of the drive pulley 45 positively engaging and braking the apparatus.

Through the pivotal movement of carrier 59 around the bolt 60, the knocking-off cam 57 has come into positive engagement with lifting flank 55 of pulley 51 and is close to (by the simultaneous operation of the brake plate 72), the apex of the lifting flank and the stop-slot 56 on it. The knocking-off cam 57 falls down then in the slot 56 of pulley 5] and stops practically instantly.

Since the knocking-off cam 57 is pivotal about the axis of journal 58, it will take the pulley 5! with it around a predetermined amount in the direction of rotation. whereby rod 71 with its guide 62 executed a corresponding pivotal movement. and the spring 64 is tensioned by the relative movement between rod 61 and guide 62.

By the insertion of knocking-off cam 57 in slot 56 of pulley 5!, the buffer means 48. carried by pulley 5!, is likewise stopped nearly suddenly. Thereby. due to the unaffected further rotation of the drive pulley 45, the spring 52 between the buffer means 47,48 is likewise tensioned. As soon as the remaining moment of gyration of the main shaft 4 no longer overcomes the force between springs 52 and 64, the main shaft 4 quickly comes to a stand-still and rotates backward almost immediately, due to the expansion of springs 52,64 about a predetermined angle to the proper stopped position.

Since the main shaft of stitch-group sewing machines is driven at constant speed and the reaction time of the brake plate 72, through control cam 70 and the shape of the lifting flank 55 is pregiven, the so called reduced speed of the main shaft and the braking pivotal movement of springs 52,64 remain constant. Thereby, the movement of the reverse motion of the main shaft is precisely determined and safe. so that. at the moment of motion reversal of the main shaft, that arm of the needle loop going to the sewing goods has glided off the lead cam 38 of knife 36 and lies in front of the cutting edge 37.

Since the knife edge 37 stands back a predetermined amount from the limiting surface 39 of the looper back 33 opposite the looper point. the arm of the thread loop going to the sewing goods is found. at the moment of reverse movement. closely in front of the blade 37, while the arm of the loop going toward the thread supply is a predetermined distance therefrom. The needle thread loop takes, at the moment of reversal of the main shaft, the position shown in FIG. 5 with respect to the looper 32 and the cutting edge 37.

During the back rotation of the main shaft, which results from the expansion of springs 52,64, the cutter 37 severs the leg of the thread loop leading to the work goods. On the other hand. the leg of the thread loop leading to the thread supply remains at a distance from the cutting edge 37 and based on its clearance and es peeially on the construction of the boundary limiting surface 39 of the looper back remains intact.

in this way the following is attained: the back rotation of the main shaft which is necessary at the end of a stopping operation to obtain prompt nullification of the oscillation moment, is utilized directly for severing the needle thread loop. The needle thread loop is so severed that a comparatively short end remains on the work goods. while for the end towards the thread supply remains intact with a sufficient length for the formation of the initial stitch of the next sewing cycle.

We claim:

1. In a chain stitch sewing machine of the type having a rotating looper with a looper point and a looper back, a main shaft, a shaft for rotating the looper, means for driving the looper shaft from the main shaft and stopping mechanism for the main shaft adapted to substantially instantaneously stop said shaft in a predetermined angular position and including means permitting a slight over-run of said shaft and subsequent recoil of said shaft to said predetermined position, in which position the thread loop is held on the looper, an improved means for cutting the thread when the machine is stopped comprising knife means attached to the back of the looper and having a cutting edge spaced above the back of the looper and arcuately extending in the direction of the point of the looper, but substantially opposite the latter with respect to the axis of the looper shaft, whereby the recoil of the main shaft during stopping drives the looper in a reverse direction to apply the cutting edge of the knife means against a leg of the thread loop held on said looper to cut the thread.

2. A chain stitch sewing machine as claimed in claim 1, wherein said cutting edge of the knife extends generally in a plane parallel to the drive shaft of the rotating looper but is concave thereto and is spaced from the side surface of the back of the looper.

3. A chain stitch sewing machine as claimed in claim 1 wherein that side of the knife means away from the cutting edge is formed as a lead cam to guide the leg of the thread loop leading to the sewing goods thereover. =l 4: k

Claims (3)

1. In a chain stitch sewing machine of the type having a rotating looper with a looper point and a looper back, a main shaft, a shaft for rotating the looper, means for driving the looper shaft from the main shaft and stopping mechanism for the main shaft adapted to substantially instantaneously stop said shaft in a predetermined angular position and including means permitting a slight over-run of said shaft and subsequent recoil of said shaft to said predetermined position, in which position the thread loop is held on the looper, an improved means for cutting the thread when the machine is stopped comprising knife means attached to the back of the looper and having a cutting edge spaced above the back of the looper and arcuately extending in the direction of the point of the looper, but substantially opposite the latter with respect to the axis of the looper shaft, whereby the recoil of the main shaft during stopping drives the looper in a reverse direction to apply the cutting edge of the knife means against a leg of the thread loop held on said looper to cut the thread.

2. A chain stitch sewing machine as claimed iN claim 1, wherein said cutting edge of the knife extends generally in a plane parallel to the drive shaft of the rotating looper but is concave thereto and is spaced from the side surface of the back of the looper.

3. A chain stitch sewing machine as claimed in claim 1 wherein that side of the knife means away from the cutting edge is formed as a lead cam to guide the leg of the thread loop leading to the sewing goods thereover.

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