US3859940A

US3859940A - Thread cutting device in a sewing machine

Info

Publication number: US3859940A
Application number: US397816A
Authority: US
Inventors: Shiroji Nakamura
Original assignee: Tokyo Juki Industrial Co Ltd
Current assignee: Juki Corp
Priority date: 1973-09-17
Filing date: 1973-09-17
Publication date: 1975-01-14
Anticipated expiration: 1992-01-14

Abstract

A thread cutting device in a sewing machine comprising a clutch member mounted on the main shaft of said sewing machine for transmitting power from a prime mover to the main shaft of the sewing machine and interrupting the power transmission, a control lever for operating said clutch member in response to the rotation of the control lever in one or the other direction, a thread cutting cam for rotation as the main shaft rotates, a reciprocal shifter so associated with the control lever that the shifter moves reciprocally in response to the rotation of the thread cutting cam during the time period from the time about one complete revolution prior to the stoppage of the main shaft to the time of stoppage of the shaft, and a thread cutting mechanism for shearing a thread in response to the reciprocal movement of the shifter.

Description

United States Patent [191 Nakamura THREAD CUTTING DEVICE IN A SEWING MACHINE [75] Inventor:

[73] Assignee: Tokyo Juki Kogyo Kabushiki Kaisha, Tokyo, Japan 22 Filed: Sept. 17, 1973 21 Appl. No.: 397,816

Shiroji Nakamura, Tokyo, Japan [52] US. Cl. 112/252, 112/67 [51] Int. Cl. D051) 3/06, DOSb 65/00 [58] Field of Search 112/65, 67, 68, 70, 73, 112/252 [56] References Cited UNITED STATES PATENTS 1,841,102 l/l932 Fifield 112/252 1,930,637 10/1933 Allen 112/252 3,051,111 8/1962 Cortese et al 112/252 3,354,852 11/1967 Kennedy et al 112/252 3,443,540 5/1969 Hannemann et a1... 112/252 3,605,664 9/1971 Hedegaard 112/252 Primary ExaminerWerner H. Schroeder Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [57] ABSTRACT A thread cutting device in a sewing machine comprising a clutch member mounted on the main shaft of said sewing machine for transmitting power from a prime mover to the main shaft of the sewing machine and interrupting the power transmission, a control lever for operating said clutch member in response to the rotation of the control lever in one or the other direction, a thread cutting cam for rotation as the main shaft rotates, a reciprocal shifter so associated with the control lever that the shifter moves reciprocally in response to the rotation of the thread cutting cam during the time period from the time about one complete revolution prior to the stoppage of the main shaft to the time of stoppage of the shaft, and a thread cutting mechanism for shearing a thread in response to the reciprocal movement of the shifter.

3 Claims, 9 Drawing Figures PATENTEB JAN 1 4 5 SHEET 6 OF 6 THREAD CUTTING DEVICE IN A SEWING MACHINE BACKGROUND OF THE INVENTION This invention relates to a thread cutting device in a cyclically operated sewing machine and more particularly, to a thread cutting device in a cyclically operated sewing machine which is adapted to start its sewing operation under control and stop in a predetermined position after a predetermined number of stitches have been formed.

l-Ieretofore, there has been proposed a thread cutting device for a cyclically operated sewing machine which comprises a control cam for controlling the number of stitches and workpiece feed in one cycle of sewing operation and a thread cutting cam for operating the thread cutting device. In this prior art thread cutting device for sewing machines, the control cam and thread cam are rotated at a reduced rotational speed for a fraction of the number of stitches to be formed in one cycle of sewing operation (for example, if the number of stitches to be formed in one cycle of sewing operation is 21, the cams are rotated at the rotational speed of as low as 1/21 the number of stitches to be formed). The thread cutting cam is designed to operate the thread cutting device from a predetermined position as determined by the number of stitches to be formed in one cycle of sewing operation. Therefore, the prior art thread cutting device is required to have thread cutting cams, the number of which corresponds to that number of stitches to be formed in one cycle of sewing operation and in consequence, it is necessary to increase or decrease the number of thread cutting cams whenever the number of stitches to be formed varies, and the thread cutting device is also required to be adjusted accordingly.

The prior art thread cutting device for sewing machines is designed for use then in only one specific type sewing machine in which a fixed number of stitches is formed in one cycle of the sewing operation. Furthermore, since several types of thread cutting cams have to be on hand for selective use in the prior art thread cutting device, the expense for the device is high. Still furthermore, the prior art thread cutting device requires much labor in assembling and adjusting, resulting in lowering of the assembly operation efficiency.

SUMMARY OF THE INVENTION The present invention is to overcome the disadvantages inherent in the prior art thread cutting device for sewing machines referred to above.

In brief, the thread cutting device for sewing machines of the present invention comprises a clutch member, mounted on the main shaft of a sewing machine in which the thread cutting device is incorporated, to transmit power from a prime mover and to interrupt the power transmission; a control lever for operating the clutch member in response to the movement of the clutch member in one direction or the other; a thread cutting cam for rotation in response to the rotation of the main shaft a pivot plate mounted on the control lever and having a shifter or roller adapted to reciprocally move in response to the rotation of the thread cam during the time period from the time about one complete revolution prior to the stoppage of the main shaft to the time of stoppage of the shaft in rela tion to the movement of a pusher member; and means for moving a movable thread cutting blade toward and away from a stationary thread cutting blade in response to the reciprocal movement ofthe pivot plate, both the movable and stationary blades being provided on the underside of a needle plate.

The thread cutting device of the present invention is versatile in that the device can be employed for sewing machines which are adapted to perform different numbers of stitches in one cycle of sewing operation. Since the thread cutting device of the invention is applicable to sewing machines which perform a different number of stitches in one cycle of sewing operation, the thread cutting device is economical and less expensive. Furthermore, since the thread cutting device of the invention does not require any additional devices and/or have to be adjusted, even if the number of stitches in one cycle varies, the sewing machine can be readily and efficiently assembled.

Therefore, one of the principal objects of the present invention is to provide a thread cutting device for sew ing machines.

Another object of the present invention is to provide a thread cutting device which is less expensive than prior devices and simple to operate.

a further object of the present invention is to provide a thread cutting device which will require less labor for adjustments and which can be efficiently assembled.

The above and other objects and attendant advantages of the present invention will be more readily ap parent to those skilled in the art from a reading of the following description in conjunction with the accompanying drawings which show one preferred embodiment of the invention for illustration purpose only, but not for limiting the scope of the same in any way.

BRIEF DESCRIPTION OF,THE DRAWINGS FIG. 1 is a front elevational view of said preferred embodiment of the device of the present invention as mounted on the rear portion of a sewing machine when the machine is in its rest position.

FIG. 2 is an end elevational view of said control device as seen at the rigth-hand end of FIG. 1.

FIGS. 3, 4 and 5 are fragmentary views of said device showing the device in its various positions i which FIG. 3 shows the positions of elements of said device when the sewing machine is in its rest position, FIG. 4 shows the positions of said elements when the sewing machine is driven at a low speed and FIG. 5 shows the positions of said elements when the sewing machine is driven at a high speed.

FIGS. 3A, 5A and 5B are fragmentary views showing the thread cutting mechnaism in its various positions. FIG. 3A shows the position of said thread cutting mechanism when the sewing machine is in its rest position; FIG. 5A shows the position of said thread cutting mechanism when the sewing machine is driven at a low or high speed; and FIG. 5B shows the position of said thread cuttingmechanism when the rotational movement from the prime mover of the main shaft of the sewing machine is interrupted.

FIG. 6 is a perspective view of said thread cutting mechanism.

PREFERRED EMBODIMENT OF THE INVENTION 'The illustrated embodiment of the invention will be described as being applied to a cyclically operable sewing machine such as bar tracking andbuttonhole sewing machines.

Referring to the accompanying drawings and more particularly, to FIGS. 1 and 2, the main shaft 1 of the sewing machine, which is rotatably supported in the framework 2 of the sewing machine, extends outwardly from said framework 2. The shaft extension supports a thread cutting cam 3, a stopper 4, a clutch assembly 5 and a pulley 6 theron in that order. The pulley 6 is rotated by an electric motor (not shown) through a suitable conventional power transmission unit (not shown) and also is axially movable along the main shaft'extension. Furthermore, the pulley 6 is normally resiliently urged rightwards as seen in FIG. 1. A control lever 8 is rotatably supported in the framework 2 by means of a shaft 7, the axis of which isparallel to that of the main shaft 1. A stopper shaft 13 is provided at the upper end with a stopper pawl 12 adapted to engage into and disengage out of a notch 11 formed in the stopper 4.

.The above-mentioned stopper shaft 13 is vertically movably supported in

support blocks

9 and 10 which also support the control lever 8. A spring 58 is disposed on the upper end portion of the stopper shaft 13 and held under compression between a member 57'fixed securely to the upper end of the shaft 13 and the support block 10. A resilient clutch plate 17 is secured to the control lever 8 by suitable means. The upper end of the clutch plate 17 is provided with an outwardly extendingportion 15 and an extension 16 which extends from the portion 15 at right angles thereto. A clutch ball 14 is held between the clutch portion and extension l5, l6 and the pulley 6. A bolt 21 extends through the slot 20 in a clutch control rocking arm 19 which extends from a part of the clutch assembly 5 and is secured to the control lever 8 to interlockthe control lever 8 with the rocking arm 19, whereby the rocking arm 19 is rotated in response to the rotation of the control lever 8.

The details of the above-mentioned clutch assembly 5 are shown in our co-pending US. Pat. Application Ser. No. 375,476, filed July 2, 1973.

By the operation of the clutch assembly 5 which is controlled by the rocking arm 19 which in turn rotates in response to the rocking movement of the control lever 8, the sewing machine in which the device of the invention is incorporated will assume the following three positions.

In the first position, the control lever 8, rocking arm 19 and clutch plate 17 assume the positions as shown in FIG. 3 wherein the transmission of rotational movement from the pulley 6 to the main shaft 1 is interrupted and as a result, the sewing machine ceases to operate.

In the second position, the control lever 8, rocking arm 19 and clutch plate 17 assume the positions as shown in FIG. 4 wherein the rotational speed of the pulley 6 is reduced and the reduced rotational movement is transmitted to the main shaft 1 to drive the sewing machine at a low speed.

In the third position, the control lever 8, rocking arm 19 and clutch plate 17 assume the positions as shown in FIG. 5 wherein the rotational movement of the pulley 6 is directly transmitted to the main shaft 1 to drive the sewing-machine at a high speed.

A spring l8'has one end secured to the control lever 8 and the other end secured to a stationary part of the sewing machine (not shown) so that the control lever 8 is normally urged in the clockwise direction as shown in FIG. 2. A support 23, the entire structure of which has a C-shape, is secured to the control lever 8 by means of a bolt or the like fastening means. The support 23 has a pair of vertically spaced upper end lower flanges through which a shaft 22 extends vertically. A stopper lever 24 has one end or the base provided with two spaced flanges positioned between the upper and lower flanges of the support 23 and is rotatably mounted on the vertical shaft 22. The base of the stopper lever 24 has also an engaging piece 25 secured thereto by suitable fastening means; A leaf spring 26 has one end secured to the control lever 8 and the other end abutting the stopper lever 24.

In FIG. 1, a control cam 27 is shown as being interlocked with the main shaft 1 and adapted to be rotated together with a workpiece feed cam 63 in the arrow A direction at a speed lower than that of the main shaft 1 so as to control the control lever 8. The sewing machine performs its predetermined sewing cycle during one complete revolution of the two cams. The peripheral surface of the control cam 27 is formed with an arcuate higher portion adapted to contact a roller 34 (of which description will be made later) while the sewing machine is being driven at a high speed, a deeper recess 28 adapted to contact the roller 34 when the sewing machine is in its rest position, and two spaced shallower recesses 29A, 298 on the opposite sides of the deeper recess 28 and adapted to engage the roller 34 during the sewing machine is being driven at a low speed. An

. L-shaped interlocking member 31 and an operation lever 32 are mounted in the framework 2 by means of I a common stepped screw 30 for movement relative to each other. The interlocking member 3l hasone arm which .rotatably supports the roller 34 at the free end thereof and another arm which is formed with an arcu- .ate slot 62. The free end of the other arm of the interlocking member 31 is formed with a hook or notch 33 adapted to engagean engaging pawl 25. The action of the spring 18 on the control lever 8 urges the roller 34 against the peripheral surface of the control cam 27 through the control lever 8, stopper lever 24 and interlocking member 31.

A second stepped screw 61 is threaded in the operation lever 32 and extends through a slot 62 in the interlocking member 31. A blocking member 60 is secured to the framework 2 by means of suitable fastening means and has one end with which a stopper 59 is inte-' grally formed for limiting the rotational movement of the operation lever 32. A chain 35 is connected at its upper end to the free end of the operation lever 32 and the lower end of the chain (not shown) is connected to an operators treadle.

The thread cutting mechanism of the sewing machine is more particularly shown in FIGS. 3A, 5A, 5B and 6.

A pivot plate or member 36 consisting of three integral arms A, B and C is pivoted at its center to the rear end face of the framework 2 by means of a stepped screw 37. The free end of the arm A rotatably supports a roller 38 in such a manner that the roller contacts the peripheral surface of the thread cutting cam 3. The arm B of the pivot plate rotatably supports a roller 39 at the free end and the arm C is pivoted at its free end to the upper end of a vertical rod 40. The lower end of the rod 40 is connected to an L-shaped link 41 (FIG. 6) which is in turn pivoted to the inner surface of the rear and lower portion of the framework 2 by means of a stepped screw 53 whereby the movement of the pivot plate 36 is transmitted to the link 41 (see FIGS. 3A and 6). A spring 52 extends between a spring anchor 51 secured to the framework 2 and a pin 50 on the link 41 as more clearly shown in FIG. 6. As shown in FIG. 6, a lever 45 is positioned under the needle plate 43 and an auxiliary lever 45' is suitably secured to one end of the first-mentioned lever 45. However, it is to be understood that the two levers can be integrally formed as a unitary structure without departing from the scope of the invention. The thus connected

lever assembly

45, 45 is pivoted on the needle plate 43 by means of a stepped screw 44. A rod 42 is connected at one end to the other end of the lever 45 and the other end of the rod is pivoted on the link 41, whereby the movement of the link 41 is transmitted to the levers 45, 45'.

A movable thread cutting knife (or movable thread cutting blade) 47 is positioned under the needle plate 43 and pivoted to the underside of the needle plate by means of a stepped screw 46. A link 48 is pivoted at its opposite ends to the auxiliary lever 45' and to the thread cutting knife 47, whereby the movement of the lever 45 is transmitted to the movable thread cutting knife 47. A stationary thread cutting knife or blade 49 is secured to the underside of the needle plate 43 to shear a thread (notshown) in co-operation with the movable blade 47.

As shown in FIGS. 3A, 5A and 58, a pushing member 56 is suitably secured to the control lever 8 and has an engaging face 54 and a recess 55 which cooperate with the roller 39 on the arm B. The engaging face 54 and recess 55 cooperate with the roller 39 in the manner described just below. The engaging face 54 continues to push up against the roller 39 during the time period of 3/4 rotation of one complete revolution of the main shaft prior to the stoppage of the sewing machine. This serves to hold the roller 38 on the arm A apart from the peripheral surface of the thread cutting cam 3. The recess 55 releases the roller 39 from its pushed-up position from the time of rotation of one complete revolution of the main shaft before the sewing machine ceases to operation and maintains the roller in the released position while the sewing machine is in its rest position. This causes the roller 38 to contact the peripheral surface of the thread cutting cam 3.

The entire sewing machine drive control device of the invention operates as follows: FIGS. 1, 2, 3 and 3A show the sewing machine in its rest position. When it is desired to drive the sewing machine from the rest position, the operator momentarily steps down on the treadle (not shown) connected to the operation lever 32 whereupon the lever 32 pivots in the clockwise direction about the screw 30 as shown in FIG. 1 until the lever abuts against the stopper 59 on the blocking member 60. Such pivotal movement of the operation lever 32 is transmitted through the stepped screw 61 to the interlocking member 31 resulting in the clockwise pivotal movement of the member 31 about the screw 30.

The clockwise pivotal movement of the interlocking member 31 causes the roller 34 at its one end to jump off the recess 28 in the control cam 27 and to move to the position in which the roller 34 comes to engage in the recess 29A. At the same time, the hook or notch 33 in the other arm of the interlocking member 31 pushes down the engaging piece 25 secured to the engaging lever 24 whereupon the engaging lever 24 is moved and at the same time, the control lever 8 fixedly connected to the engaging lever 24 pivots through a small angular distance in the counter-clockwise direction about the shaft 7 as seen in FIG. 2. As a result, the stopper pawl 12 which was engaged in the notch 11 in the stopper member 4 clears the notch 11 as shown in FIG. 4. The pivotal movement of the control lever 8 in the counterclockwise direction moves the pushing member 56 secured to the control lever 8 so as to cause the engaging face 54 on the pushing member to push the roller 39 on the pivot plate 36 upwardly so as to move the roller 38 away from the peripheral surface of the thread cutting cam 3. The rocking arm 19 is slightly moved in response to the pivotal movement of the control lever 8 as shown in FIG. 4 whereby the rotational movement of the pulley 6 is transmitted to the main shaft 1 through the clutch assembly 5 at a reduced rate. Thus, the sewing machine is initially driven at a low speed and the cam 27 starts to rotate in the arrow direction A at the same low speed as the sewing machine. As the cam 27 rotates in the arrow direction A, the roller 34 at one arm of the interlocking member 31 contacts the recess 29A in the cam 27 and pushes the cam in response to the rotation of the cam. While the roller 34 is in contact with the recess 29A, the lever 8 is maintained in the position in which the sewing machine is driven at a low speed. As the cam 27 interlocking with the sewing machine rotates further, the roller 34 is pushed up from the recess 29A onto the non-recessed portion of the peripheral surface of the cam 27. As a result, the interlocking member 31 is further pivoted in the clockwise direction thereby moving the control lever 8 to the position as shown in FIG. 5. Such movement of the control lever 8 pivots the rocking arm 19 further whereby the rotational movement of the pulley 6 is transmitted to the main shaft 1 through the clutch assembly 5. As a result, the sewing machine is continuously driven at a high speed while the roller 34 is on the non-recessed portion of the peripheral surface of the control cam 27 thus forming a cycle of operation and forming a seam. Just before the cyclic seam formation operation is completed or just before the control cam 27 completes one complete revolution, the roller 34 on the interlocking member 31 rides on and moves along the recess 293 in the control cam 27 whereby the interlocking member 31 is pivoted about the screw 30 in the counter-clockwise direction as seen in FIG. 2. As a result, the hook or notch 33 in the other arm of the interlocking member 31 releases its oppressive force from the engaging piece to allow the control lever 8 to pivot from the position in FIG. 5 to the position in FIG. 4 by the action of the spring 18. As the control lever 8 moves in the manner as mentioned just above, the rocking arm 19 is pivoted so as to transmit the rotational movement of the pulley 6 to the main shaft 1 through the clutch assembly 5 at a reduced rate so as to drive the sewing machine at alow speed.

Therefore, before the main shaft 1 rotates about onefourth of one complete revolution prior to the stoppage of the sewing machine in a predetermined position, the roller 34 on the interlocking member 31 drops into the recess 28 in the cam 27. As the interlocking member 31 is further pivoted in thisway, the hook 33 of the interlocking member 31 clears the engaging face and as a result, the control lever 8 is moved from the position in FIG. 4 to the position in FIG. 5B. This pivotal movement of the control lever 8 interrupts the transmission of the rotational movement of the pulley 6 to the main shaft 1 and prepares for the thread cutting and stopping of the sewing machine in the predetermined position. More particularly, as the rocking arm 19 which is now in the position of FIG. 4 further pivots in response to the pivotal movement of the control lever 8 to interrupt the transmission of the rotational movement of the pulley 6 to the main shaft 1, the stopper pawl 12 contacts the peripheral surface of the stopper member 4 to prepare for the stoppage of the main shaft 1. As the pusher member 56 moves together with the control lever 8, the roller 39 on the pivot plate 36 is released from the engaging face 54 on the pusher member 56 which is now pushing the roller upwardly to move it to a position above the recess 55 in the pusher member, and thus, the roller 38 is caused to contact the peripheral surface of the thread cutting cam 3 by the force of the spring 52 acting on the rod 40. The main shaft 1 rotates about A of one complete revolution from the position of FIG.

53 to the position of FIG. 3B by force of inertia.

During the rotation of one complete revolution of the main shaft 1 by force of inertia, the thread cutting mechanism operatesto shear the thread and the main shaft 1 then stops in its predeterminedposition.

' During the initial rotation of about i of one complete revolution of the main shaft 1, the pivot plate .36, which is now in the position of FIG. 6, is pivoted in the counter-clockwise direction because the roller 38 moves into the recess in the thread cutting cam 3. The pivotal movement of the pivot plate 36 is transmitted through the rod 40, link 41, rod 42, lever 45 and link 48 to the movable threadcutting blade 47 whereupon the blade 47 pivots in the clockwise direction as seen in FIG. 6 and the thread selected to be sheared (the thread may be the thread on the needle or bobbin as the case may be) is sheared off. Thereafter, as the roller 38 is forced out of the recess in the thread cutting cam 3, the pivot plate 36 pivots in the clockwise direction as seen in FIG. 6 whereby the'thread cutting blade 47 pivots in the direction opposite to the aforementioned direction or the counter-clockwise direction to cooperate with the stationary blade 49 to shear the selected thread. After the thread cutting operation as mentioned just above, the stopper pawl 12 engages in the groove 11 in the stopper member 4 as shown in FIG.

3A to stop the main shaft 1 in the predetermined posi-.

tion. 4

The lever 24 is adapted to stop the sewing machine while the machine is performing a cycle of the seam forming operation. For that purpose, the lever 24 is urged rightwards (as seen in FIG. 1), while the sewing machine is being driven at a high speed. When urged rightwards, the lever 24 pivots about the shaft 22 to disengage the engaging piece 25 on the lever 24 from the hook 33 on the interlocking member 31 whereupon the control lever 8 which is now in the position of FIG. 5 is urged in the clockwise direction as seen in FIG. 5 by the force of the spring 18 to the position of FIG. 3 in which the lever is rest.

The afore-mentioned mechanism transmits the rotational movement of the electric motor to the sewing machine at the same speed as the motor, however, this reduced speed and interruption of movement transmission may be substituted for by any other conventional mechanism. For example, such a mechanism may be the belt shifting-type mechanism as disclosed in U.S. Pat. No. 3,216,381. The mechanism may be also the so-called pole-changemotor in which the number of rotation of an electric motor per unit time is varied by varying the number of poles. When employed in the control device of the invention, the belt shifting mechanism or pole change motor is controlled inrelation to the pivotal movement of the interlocking member or control lever 8.

The afore-mentioned mechanism which is adapted to stop the sewing machine in its predetermined position may be also substituted by any other conventional mechanism. For example, the mechanical locking system 29 as disclosed in U.S. Pat. No. 3,216,381 may be employed for that purpose.

Although only one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood'that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is': Y

l. A thread cutting device for cyclically operated sewing maching having primary mover means and a mainshaft, said thread cutting device comprising a clutch member mounted on said main shaft for transmitting and interrupting power'from said primary mover means to said main shaft;

a control means rotatably mounted on the framework of said sewing machine and coupled with said clutch member for controlling the rotational movement of said main shaft being rotated by said primary mover means; I

a thread cutting cam rotatably mounted on said main shaft and adapted to be rotated in response to the rotational movement of said main shaft;

pivot plate means pivotally mounted onto said sewing machine frame for being contacted by said control means and operatively positioned for contacting the thread cutting cam at predetermined time intervals in response to movement of the pivot plate means by the control means and for being reciprocally pivoted while in contact with the rotating thread cutting cam; and

thread cutting means operatively connected to said pivot plate means for cutting the thread in response to the reciprocal pivoting movement of said pivot plate means.

2. A thread cutting device as claimed in claim 1,

wherein said control means includes a lever having a pusher member with cam faces secured thereto for contact with said pivot plate.

3. A thread cutting device as claimed in claim 2, wherein said pivot plate is comprised of a first arm hav ing a roller for cooperating with the cam faces of said pusher member, a second arm having a roller for conta'cting the peripheral surface of said thread cutting cam, and a third arm operatively connecting said pivot 5 plate to said threadcutting machine.

Claims

1. A thread cutting device for cyclically operated sewing maching having primary mover means and a mainshaft, said thread cutting device comprising a clutch member mounted on said main shaft for transmitting and interrupting power from said primary mover means to said main shaft; a control means rotatably mounted on the framework of said sewing machine and coupled with said clutch member for controlling the rotational movement of said main shaft being rotated by said primary mover means; a thread cutting cam rotatably mounted on said main shaft and adapted to be rotated in response to the rotational movement of said main shaft; pivot plate means pivotally mounted onto said sewing machine frame for being contacted by said control means and operatively positioned for contacting the thread cutting cam at predetermined time intervals in response to movement of the pivot plate means by the control means and for being reciprocally pivoted while in contact with the rotating thread cutting cam; and thread cutting means operatively connected to said pivot plate means for cutting the thread in response to the reciprocal pivoting movement of said pivot plate means.

2. A thread cutting device as claimed in claim 1, wherein said control means includes a lever having a pusher member with cam faces secured thereto for contact with said pivot plate.

3. A thread cutting device as claimed in claim 2, wherein said pivot plate is comprised of a first arm having a roller for cooperating with the cam faces of said pusher member, a second arm having a roller for contacting the peripheral surface of said thread cutting cam, and a third arm operatively connecting said pivot plate to said thread cutting machine.