US3921554A - Thread-trimming device on a sewing machine - Google Patents

Abstract

An improved thread cutting device is disclosed for trimming the upper and lower threads in a straight lock stitch sewing machine. The device is positioned at the closest possible position above the rotary hook and is operatable in two different speeds for preparatory and thread-trimming operations, respectively.

Description

' United States Patent Uozaki et al.

[ 1 Nov. 25, 1975 1 THREAD-TRIMMING DEVICE ON A SEWING MACHINE [75] Inventors: Seizo Uozaki, Toyota; Hitoshi Sakashita, Aichi, both of Japan [73] Assignee: Aisin Seiki Kabushiki Kaisha,

Kariya, Japan [221 Filed: May 29, 1974 [21] Appl. No.: 474,462

[30] Foreign Application Priority Data May 30, 1973 Japan 4861376 [52] US. Cl. 112/252 [51] Int. C1. D058 65/02 [58] Field of Search 112/252 [56] References Cited UNITED STATES PATENTS 3,141,432 7/1964 Reeber et a1. 112/252 3,173,392 3/1965 Hedegaard 112/252 3,173,393 3/1965 Adam 112/252 3,371,633 3/1968 Hedegaard 112/252 3,443,540 5/1969 Hannemarm et a1 112/252 3,756,177 9/1973 Landwehr 112/252 3,776,161 12/1973 Papajewski 112/252 Primary ExaminerGeorge l-l. Krizmanich Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak 4 Claims, 12 Drawing Figures U.S. Patent Nov. 25, 1975 Sheet 1 of3 3,921,554

U.S. Patent Nov. 25, 1975 Sheet 3 of3 3,921,554

THREAD-TRIMMING DEVICE ON A SEWING MAGI-IINE This invention relates generally to industrial straight lock stitch sewing machines. More specifically, it relates to improvements in and relating to threads trimming device.

An object of the present invention is to provide the threads trimming device workable at the best operating phase and at the closest possible position to the conventional rotary hook.

A further object of the invention is to provide the threads trimming device of the above kind, adapted for positive prevention of the blowing-out of the upper thread before the catching thereof for the trimming job.

These and further objects, features and advantages of the invention will be made more apparent with the following detailed description of the invention by reference to the accompanying drawings illustrative of a preferred embodiment thereof.

In the drawings:

FIG. 1 is an inverted plan view of essential parts of the thread-cutting device according to the present invention from the bottom side of the machine bed.

FIG. 2 is a perspective view of the essential parts of the thread-cutting device according to the invention.

FIG. 3 is a front elevation of the thread-cutting device when seen from the front side of the machine bed which is shown in chaindotted line.

FIG. 4 is a perspective view of a tension release mechanism cooperating with the threadcutting device.

FIG. 5 is a partial sectional elevation of a needle bar together with a part of the machine arm, specifically illustrating a timing mark provided on the needle bar.

FIG. 6 is an enlarged detail side view of a pair of partial gears employed in the thread-cutting device shown at a timing in coincidence of that of the needle bar shown in FIG. 5.

FIG. 7 is a partial sectional front view of a thread catcher included and cooperating with a conventional rotary hook, the scale being slightly enlarged from that of FIG. 3 and the timing being such that the thread catcher begins to catch the sewing thread.

FIG. 8 is a similar view to FIG. 6, wherein, however, the timing is same as in FIG. 7.

FIG. 9 is a similar view to FIG. 7, wherein, however, the thread catcher has caught the sewing yarn.

FIG. 10 is a similar view to FIG. 6, wherein, however, the timing corresponds to that employed in FIG. 9.

FIG. 11 is a similar view to FIG. 7, wherein, however, the timing is such that the thread cutter has just cut the thread.

FIG. 12 is a similar view to FIG. 6, wherein, however the timing corresponds to that employed in FIG. 11.

In the following, a preferred embodiment of the invention will be described in detail by reference to the accompanying drawings.

In FIGS. 1 3, numeral 1 denotes schematically and partly in phantom manner a machine bed, a mounting frame 2 being fixedly attached on a lower surface of said bed by means of set screws 3 and 4. A shaft 6 having an operating rigid lever portion 5 is mounted rotatably on the frame 2 at 2a and 2b. The shaft 6 is further provided rigidly with an enlarged flange 7 attached thereto by means of a set screw 8. As seen, especially from FIG. 2, the shaft 6 is formed with a shoulder 9 for 2 the prevention of occasional axial shift of the shaft, said flange 7 serving for the same purpose.

A coil spring 10 is mounted on and between a part of said frame and radial projection 7a of said flange 7. In the case of off-service position of the thread cutter device to be described, said radial projection 7a is kept in engagement with a stationary stop 11 as shown in FIGS. 1 and 2, said stop being fixedly positioned by being threaded through a portion of said frame.

Numeral 12 represents a partial gear toothed only at and mounted loosely on said shaft 6. This partial gear is formed with an axially projecting boss 12a which is formed in turn with an axial slot 14 slidably receiving an axial projection 13 projecting rigidly from said flange 7. Partial gear 12 is slidable axially on the shaft 6, but its rotation is made in unison therewith, by virtue of the fixed mounting of the flange 7 on the shaft.

Arm member 15 is mounted loosely on the shaft 6, said member 15 being formed with a recess 16 kept normally in engagement with the tip end of a plunger 19 of thread-cutter solenoid 18 which is fixedly mounted on a part of said frame 2 by means of a plurality of set screw 17. Therefore, the arm member 15 can not rotate normally integral with the shaft 6, even if the latter is caused to rotate.

It will be seen from the foregoing that when solenoid 18 is energized by supply of electric current from a current source, not shown, thereto for the execution of a thread-cutting job, plunger 19 is caused to advance leftwards in FIG. 1, so as to push the partial gear 12 and flange 7 in the same direction against the action of a coil spring 20 provided between the last mentioned two members.

Numeral 22 represents a thread-release cable passing through a small hole formed through one end of said arm member 15 and fixedly attached thereto by a pair of fixing elements 23 and 23. A flexible cable sheath 102 slidably guides the cable 22 and is attached fixedly at its one end to a stationary member 103 by means of a clip 104, said member 103 being rigid with the solenoid 18.

Numeral 24 represents only partially a conventional hook shaft which is supported rotatably at its one end shown by a bearing 25 press fit in position into the bed 1 A pivotable holder 26 is provided in close proximity of the left end of the bearing metal, FIG. 1, but it is pre vented from its axial movement by virtue of the provision of stop spring 27. The holder 26 and the lever portion 5 are pivotably connected with each other by a link member 28 and stepped screws 29 and 31).

A stationary cutter blade 32 and a thread guide plate 33 are fixedly attached to the bed 1 by means of a set screw 31. The cutter blade 32 is arranged in opposition to a thread catcher 35 which is fixedly attached to the holder 26 by a set screw 34., in such a way that the cutting edge 41 formed on the cutter blade and that at 40 formed on thread catch 35 can be brought into a shearing relationship for performing a thread-cutting job, as will be described later more fully.

The free end portion of thread guide plate 33 has an arc-shape in its side view, said arc being designed and arranged concentrically with a conventional rotary hook 36. This thread guide plate 33 is arranged to occupy an intermediate position when seen in the radial direction of the rotary hook, as most clearly seen from FIG. 7. The plate 33 is further provided with an opening 97 adapted for passage of the sewing thread so as to keep the part of the latter in coincidence with the center of the needle.

The thread catcher 35 comprises as its effective portion an arc-shaped portion made concentric to the ro' tary hook and is formed with a pointed and portion 37 followed reversedly by a thread-engaging portion 38 which is further followed reversedly by a londitudinally grooved portion 39 terminating into a cutting edge 40. This movable cutting edge 40 is adapted for cooperating with a cutting edge 41 formed on the tip end of stationary cutting element 32 for performing a thread-cutting job, as will be more fully described hereinafter.

Hook shaft 24 is attached fixedly with a driving partial gear 42 by means of a set screw 43, said partial gear representing drive teeth at 98, as shown in FIGS. 6, 8, l and 12. In succession to these drive teeth 98, the partial gear 42 represents on its outer periphery a cam portion 92 having a gradually increasing radius of curvature. In further succession to this cam portion 92, the partial gear 42 represents a blank peripheral surface 99 terminating at said teeth 98.

The driving partial gear 42 having the aforementioned structure will rotate only in idle and in unison with the hook shaft 24 during the normal sewing operation of the machine. However, when the solenoid 18 is energized for initiating a thread-cutting job, the partial gear 12 is caused to slide in the aforementioned way so that the latter is brought into lateral registration with the companion partial gear 42 adapted for engagement with each other during the rotational movement of hook shaft 24.

A tension-release lever 45 and a pivotable member 46 are pivotably mounted on the conventional machine arm 44 by means of a common pivot pin 47, although the set position has been omitted from the drawing. As shown in FIG. 4, tension release lever 45 is formed with a cam surface 48 which is adapted for acting upon a pin or tension stud 49 with rotation of said lever, so as to release the tension of the upper thread at the tension disc unit 50 of the known structure, as in the commonly known way.

The cable guide sheath 102 fixedly attached at its one end to the frame 2 as shown and described hereinbefore in connection with FIG. 1, has its opposite end is fixedly attached to the machine arm 44, although not specifically shown. The cable 22 slidable in and along the sheath 102 has its one end fixedly attached to the upper or motion-receiving end of the tension release lever 45 as shown in FIG. 4. By the sliding movement of arm member with energization of the solenoid 18 in the aforementioned manner, the lever 45 is pulled by the cable against the spring action at 51 so that the latter is caused to rotate in clockwise about its pivot 47 in FIG. 4 for the execution of the tension-releasing job, as was described hereinbefore. On the contrary, when the solenoid 18 is de-energized, the accumulated energy in the spring 51 is released, thereby the lever 45 is rotated in the counter clockwise direction in FIG. 4 so that the cam surface 48 is disengaged from contact with the motion-receiving end of the pin or stud 49.

When the commonly known lifting plate 52 is lifted by means of knee lifter, as an example, the rotatable member 46 is caused to rotate for pushing a pointed projection of thread tension release lever 45, so as to release upper thread tension, and indeed, by virtue of the fork joint between pin 53 and fork 54 of the rotatable member 46.

As shown in FIG. 5, conventional needle bar 94 carrying a needle and reciprocated by a crank mechanism, not shown, by the rotation of a conventional upper or arm shaft, not shown, is given a timing mark shown at 95, being selected at a predetermined position on the needle bar. In the present case, when the mark 95 is brought into coincidence with the lower end of needle bar metal 96 as shown, the needle bar will occupy a position of about 55 degrees in advance of the upper dead point of the needle bar 94.

As commonly known, the thread tension disc unit 50 is mounted on the front side of the machine arm in close proximity of the free end extremity of the latter as commonly employed, although not specifically shown.

The general operation of the thread trimming device so far shown and described is as follows.

When the sewing machine operator operates a manually operable means for stopping the high speed sewing operation, the foot-operated pedal in this case, is released from its operating position, a clutch is disengaged from the main drive electric motor and a brake is applied to the shafting system including, as known, the upper shaft, not shown, for driving the needle bar 94, and the hook shaft 24, for stopping the rotation of these shaft. In this case, the needle bar 94 is brought into and held just at its lower dead point by actuation of a needle position-sensing and a source-curre interruption means, not shown, which are known per se.

When the operator depresses the foot pedal in the reverse direction, an electric speed slow-down means, not shown, is operated as known per se, and the upper and the lower or hook shaft are caused to rotate at a respective slower constant speed which is selected to l/30 of the higher sewing speed. In this way, the needle bar 94 moves upwards from its lower to upper dead point. Before arrival of the needle bar at its upper dead point, a known sensor is brought into operation and the trimming solenoid 18 is energized, thereby its plunger 19 being operated to push the arm member 15 and partial gear 12 axially in the aforementioned way for bringing the partial gear 12 into registration with its companion partial gear 42 ready for mutual engagement. With rotation of the hook shaft 24 and the needle bar is brought to about 55 degrees, when shown in terms of the crank angle, before its upper dead point, the drive partial gear 42 is brought into engagement with the follower partial gear 12, thus rotation being transmitted from the former to the latter as shown in FIG. 6. Thus, motion is further transmitted through arm member 7, shaft 6, lever 5 and link 28 to holder 26. This holder begins to rotate for causing the thread catcher 35 to initiate a thread-trimming operation.

Then, two partial gears 12 and 42 take mutually the next timed phase shown in FIG. 8 wherein the pointed projection 37 of thread catcher 35 invades into the loop of upper thread N formed by the rotary hook 36, for catching the thread, as schematically shown in FIG. 7. At the same time, the thread-engageable portion 38 of thread catcher 35 catches and draws out the lower thread B extending the bobbin case 91 housed as conventionally within the rotary hook.

At a still further advanced timed phase for the mutually engaging partial gears 12; 42 as shown in FIG. 10 where they have been completed a partial revolution due to the gear tooth meshing, the upper thread N is subjected to a upwardly directing drawing action by the conventional thread take-up lever, not shown. But, in this case, the upper thread is held by the thread catcher 35 by being engaged thereby, so as to leave a proper end length of the thread, enough for avoiding a slip-out of the thread from the thread eyelet, not shown, of needle 94a replaceably attached to needle bar 94, at the commencement of the next sewing job. At this stage, the lower thread B, together with a part of the upper thread which lies close to the sewing material, not shown, runs in and along the groove 39 upon leaving from the thread catcher 35, thus being prevented from cutting by contact with the cutting edge 41 of stationary knife 32. Therefore, a proper length of the lower thread as necessary for later use upon thread-trimming and reinitiation of a new sewing job can be drawn out from the bobbin case 91 and preserved in position.

As the timing of the operational stage shown in FIGS. 9 and 10 corresponds to 60 70 in advance of the arrival of the upper dead point of thread take-up lever, a considerable difficulty will occur by the invitation of an excess upward pulling of the trimmed upper thread by the upwardly moving thread take-up lever towards its upper dead point to such a degree that the thread slips off the needle, thereby making the next succeeding sewing operation impossible, if the upper thread should have been trimmed directly after the completion of the aforementioned thread catch operation. On the other hand, if the thread catcher should be moved over a substantial distance after the aforementioned execution thread-catching operation by the latter, it must be necessary to overcome a considerable amount of resistance provided by the part of the upper thread extending from its supply source to the catcher 35 even if the thread tension at the tension disc unit 50 has been released. Even if the upper thread should not have been broken unintentionally in this case, the thread-trimming device will require a considerably large amount of driving force when operating under these conditions. According to the present invention, these otherwise unavoidable conventional drawbacks can be substantially obviated.

In the proposed design and arrangement of the thread-trimming device according to this invention,

such excess drawing-out of the upper thread can effectively avoided by bringing the gear teeth 98; 100 partial gears 12; 42, respectively, into mutual engagement so that the movable cutting edge of the catcher 35 and the stationary cutting edge 41 of the stationary knife 32 may be brought rapidly at a highly close distance therebetween directly before the arrival of the specific operational timing stage shown in FIG. 10, thereby bringing the occurrence of a thread-trimming operation as close as the realization time of the upper dead point of the thread take-up lever. Thence, the drive partial gear 42 will rotate in such a way that the cam surface 92 formed in succession to the gear teeth 98 thereon keeps in sliding contact with the last one of the teeth 93 on the companion partial gear 12. By this operation, the cutting edges 40; 41 are brought into cooperation with each other, as shown in FIGS. 11 and 12, for simultaneous trimming of these threads N and B and until the practical realization of this trimming job, the thread catcher 35 shifts at a rather low speed, so as to obviate the aforementioned drawbacks.

Upon execution of the aforementioned thread-trimming job and after further slight rotation of partial gear I 42, the engagement of cam surface 92 of partial gear 42 and the gear tooth group 93 is released. After release of the binding operation by the partial gear 42, the thread catcher 35 will return under the spring force at 10 until its arm 7 is brought into contact with stop screw 11 After realization of this phenomenon, a known position sensor, not shown, will act to sense the beforehand scheduled upper stop position of the thread take-up lever which has been set to a position close to its upper dead point, so as to deliver an electrical instruction signal for the interruption of electric current supply to the trimming solenoid 18. In this way, partial gear 12, arm 15 and plunger 19 are caused to return to their starting position by the resilient resetting action provided by the coil spring 20.

Under these conditions, therefore, the thread-trimming device is kept ineffective and ready for the next trimming operation, even if the sewing machine by caused to run for its regular and renewed sewing job.

At the same time with the pushing movement of the actuated plunger 19 upon arm member 15 for the execution of the thread-trimming job, cable 22 is also pulled in the aforementioned way, so as to rotate the tension release lever 45, FIG. 4, for pushing the stud 49 towards thread take-up disc unit 50 by means of cam surface 48 on the lever, resulting in the tension release of the thread at the unit. The thread N will be delivered, therefore, in a smooth manner from its supply source, even if the thread take-up lever makes its thread pull-up operation after successful catch of the upper thread N by the catcher 35, as schematically shown in FIG. 9.

After completion of the thread-trimming job and upon interruption of current supply to solenoid 18, the tension release lever will be caused to swivel in the opposite or counter clockwise direction in FIG. 4 under the action of return spring 51, so as to bring the thread take-up disc unit into its operating position for tightening the upper thread N.

Next, the operation of the thead guide plate 33 will be described hereinbelow.

Upon lapse of the timing as represented by FIG. 7, the upper thread N drawn-in by rotary hook 36 will be urged to disengage from the latter as a result of the upward pull exerted upon the thread by the thread takeup lever, not shown. As a result, the upper thread may sometimes reep up substantially in the peripheral direction of the hook 36 and could be held far from the pointed projection of the catcher 35 which is now trying to catch the thread. As a result, the upper thread could not be subjected to the necessary trimming job at and between the cutting edges of the stationary and moving cutter knife elements. Or even if trimmed, a shorter length of thread end only could be preserved.

With use of the thread guide plate 33 having an eye opening at 97, the upper thread loop being upwardly pulled by the thread pick-up lever is drawn-to by the rotary hook 36 only after once passing through that opening. Therefore, the aforementioned defective large reep-out movement of the: thread in the peripheral direction of hook 36 can be prevented and a guaranteed thread catch may be positively assured.

The trimmed end of the lower thread B is limited by the same opening 97 from its free movement, the upper thread N can pick up necessarily the lower thread B at the commencement of the next regular sewing operation.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. A thread-trimming device for an industrial sewing machine, comprising:

a. a first shaft rotatably driven by a main shaft of the machine;

b. first ratchet means disposed upon said first shaft and rotatable therewith;

c. stationary blade means fixedly secured to the framework of said machine;

d. a second shaft disposed parallel to said first shaft;

e. pivotably movable blade means connected to said second shaft;

f. second ratchet means disposed upon said second shaft and being axially movable relative thereto so as to selectively engage said first ratchet means; and

g. electrically operated means for moving said second ratchet means along said second shaft so as to engage said first ratchet means, whereby said second shaft will be rotated so as to move said movable blade means relative to said stationary blade means to perform the thread trimming operation.

2. A thread-trimming device for an industrial sewing machine according to claim 1, wherein said first ratchet means comprises a first partial gear having teeth on only a portion of the periphery thereof and a cam surface successively disposed from said toothed gear portion; and said second ratchet means comprises a second partial gear having teeth on only a portion of the periphery thereof, whereby upon actuation of said electrically operated means, the toothed portions of said first and second partial gears are engaged with each other to rapidly rotate said movable blade means to an operable position relative to said stationary blade means and thereafter, said cam surface of said first partial gear portion comes into sliding contact with said second partial gear to slowly rotate said second blade means to cooperate with said first blade means to thereby perform the thread trimming operation.

3. A thread trimming device according to claim 2, wherein said movable blade means comprises:

a. thread catching means for drawing and catching the lower thread out of a bobbin case of said ma chine for preparing said thread trimming operation, and

b. a blade portion for cooperating with said first stationary blade means to perform said thread trimming operation.

4. A thread trimming device according to claim 3, wherein said stationary blade means include a thread guide plate secured to said framework of said machine, said guide plate having a thread guiding hole through which pass upper and lower threads for assuring said thread trimming operation and the commencement of the following regular sewing operation.

Claims (4)

1. A thread-trimming device for an industrial sewing machine, comprising: a. a first shaft rotatably driven by a main shaft of the machine; b. first ratchet means disposed upon said first shaft and rotatable therewith; c. stationary blade means fixedly secured to the framework of said machine; d. a second shaft disposed parallel to said first shaft; e. pivotably movable blade means connected to said second shaft; f. second ratchet means disposed upon said second shaft and being axially movable relative thereto so as to selectively engage said first ratchet means; and g. electrically operated means for moving said second ratchet means along said second shaft so as to engage said first ratchet means, whereby said second shaft will be rotated so as to move said movable blade means relative to said stationary blade means to perform the thread trimming operation.

2. A thread-trimming device for an industrial sewing machine according to claim 1, wherein said first ratchet means comprises a first partial gear having teeth on only a portion of the periphery thereof and a cam surface successively disposed from said toothed gear portion; and said second ratchet means comprises a second partial gear having teeth on only a portion of the periphery thereof, whereby upon actuation of said electrically operated means, the toothed portions of said first and second partial gears are engaged with each other to rapidly rotate said movable blade means to an operable position relative to said stationary blade means and thereafter, said cam surface of said first partial gear portion comes into sliding contact with said second partial gear to slowly rotate said second blade means to cooperate with said first blade means to thereby perform the thread trimming operation.

3. A thread trimming device according to claim 2, wherein said movable blade means comprises: a. thread catching means for drawing and catching the lower thread out of a bobbin case of said machine for preparing said thread trimming operation, and b. a blade portion for cooperating with said first stationary blade means to perform said thread triMming operation.

4. A thread trimming device according to claim 3, wherein said stationary blade means include a thread guide plate secured to said framework of said machine, said guide plate having a thread guiding hole through which pass upper and lower threads for assuring said thread trimming operation and the commencement of the following regular sewing operation.

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