US3191562A

US3191562A - Thread trimming device

Info

Publication number: US3191562A
Application number: US233242A
Authority: US
Inventors: Samuel R Frankel
Original assignee: American Safety Table Co Inc
Current assignee: American Safety Table Co Inc
Priority date: 1962-04-16
Filing date: 1962-10-26
Publication date: 1965-06-29
Anticipated expiration: 1982-06-29
Also published as: CH411540A

Description

June 29, 1965 s. R. FRANKEL.

THREAD TRIMMING DEVICE original Filed April 1o, 195s 6 Sheets-Sheet 1 s. R. FRANKEL THREAD TRIMMING DEVICE original Filed April 1o. 1959 June 29, 1965 6 Sheets-Sheet 2 lrivenor: SAMUEL R. FEP'NKER Py-Hfcrnej June 29, 1965 THREAD TRIMMING DEVICE Original Filed April l0, 1959 6 Sheets-Sheet 3 ,..4 I wgo us SSSL r 's4 IZI "yl-JP; u2 7 8o n IOS MJ Invszr-or;`

Samuel. R-FRP'N HEL BYXMM June 2 9, 1965 s. R. FRANKEL 3,191,562

THREAD TRIMMING DEVICE Original Filed April l0, 1959 6 Sheets-Sheet 4 Inward-or;

SPmuEk E. FRANKEL.

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Af-fol'ney June 29, 1965 s. R. FRANKEL 3,191,552

THREAD TRIMMING DEVICE Original Filed April 10, 1959 6 Sheets-Sheet 5 lnverli'ov:

51m/wak RFRHNKEL- PH'TOrney June. 29, 196s s. R. FRANKEL Y 3,191,562

THREAD TRIMMING DEVICE Original Filled April 10, 1959 6 Sheets-Sheet 6 *isonsllooM-f-ssoMS--l SVHTCH |07 swrrcn log Ms soon soon -I swrrcmoe v lnvenkfor:

SAMUEL RFRHNKEL HHforney United States Patent Office 3,191,562 Patented June Z9, 1965 3,191,562 THREAD TRIMMING DEVICE Samuel R. Frankel, siiillington, Pa., assignor to American Safety Table Company, Inc., Mohnton, Pa., a corporation of Pennsylvania 1 Continuation of'papplication Ser. No. 805,640, Apr. 10, 1959. This application Oct. 26, 1962, Ser. No. 233,242 27 Claims. (Cl. 112-252) This invention relates to thread trimming devices for sewing machines, and more particularly relates to a device for cutting both the needle thread and the bobbin thread at points very close to the outer surfaces of the material being stitchedso that a later final trimming of such threads is not required, this application being a continuation of my pending application, Serial No. 805,640, filed April 10, 1959, now abandoned. i

In commercial operations utilizing sewing machines for the mass production of stitched articles, such as in the garment trades, the sale price of the stitched articles produced is necessarily related to the labor cost involved in producing such` article. Accordingly, reductions in the fabrication time of a stitched'article result in the ability to sell such article at a lower price, and labor saving devices are therefore of great interest to the trade. During the stitching process, it is frequently necessary to sever the needle and bobbin threads While the fabric being stitched is centrally located relative to the needle, that is, when the line of stitching does not terminate at or near the edge `of the fabric. Generally, in such a case, the work must be displaced from its position at the end of the line of stitching so that Vsufficient of the needle and the bobbin threads become available for hand cutting, the work then being repositioned to the proper place for starting the next line of stitching. After the stitching operations have all been completed it is then necessary to trim olf all of the projecting thread ends so that the stitched article may present a neat and finished appearance. Such a thread trimming operation is time consuming and can contribute materially to the labor costs associated with theproduction of a particular stitched article.

In order to :alleviate this thread-trimming proble-m, attempts have been made in the past to provide automatic thread cutting means designed to leave a minimum of thread to be trimmed, and which in some cases could be ignored. One such thread cutting means has been mounted to the rear of the presser foot to cut the thread by a vertical down stroke of a cutting edge. This type of apparatus, of course, could only be used at the edge of a fabric where the fabric is shifted out from under the needle and behind the vertical cutting device, in order that the cutting stroke should cut only the threads and not the underlying fabric as well; The vertical cutting devices are therefore of limited use, being helpful only in those cases where the line of stitching terminates at the edge ofthe stitched article.

Other mechanical cutting arrangements have been devised which cut the threads by a cutting stroke in a plane parallel to the surface of the fabric being stitched. Such devices can of course be utilized when the fabric is centrally located under the needle without requiring that the fabric be removed from the sewing machine. However, even cutters of this latter type leave thread ends of approximately one-eighth of an inch and the need for subsequent hand trimming of these short ends remains. My invention, on the other hand, provides for cutting of the needle and bobbin threads within approximately twohundredths of an inch of the fabric surfaces and consequently completely eliminates the need for subsequent hand trimming, thus effecting a material saving i-n time.

Briefly, my invention accomplishes thread cutting by apparatus including a pair of hot wires which rapidly burn through the threads to be severed. One of these wires is associated with the presser foot and serves to sever the needle thread, while the other wire is associated with the throat plate above the bobbin and serves to sever the bobbin thread. These hot wires are only energized when so desired by the sewing machine operator, so that during a normal stitching operation there is no tendency whatever for needle thread and bobbin thread to be prematurely severed.

My invention also includes means for insuring that the sewing machine may be again immediately utilized after a thread cutting operation without having to rethread the needle. The thread cutting operation is carried out in a particular sequence of steps which follow one another automatically when the thread cutting operation is initiated. Accordingly, it is a primary object of my invention to provide a novel thread cutting apparatus effective when actuated to sever the needle thread and the bobbin thread of a sewing machine very close to the outer surfaces of an article being stitched, to thereby eliminate the need for subsequent hand trimming of short thread ends. A

It is another object of my invention to provide a novel thread cutting apparatus for severing the needle thread andbobbin thread of a sewing machine close to the surfaces of a stitched article by means of operator controlled and selectively energizable hot wires.

Yet another object of my invention is to provide novel thread cutting apparatus which permits the needle thread and bobbin thread associated with the sewing machine to be cut without displacing the article being stitched from the position it occupies at the end ot the stitching operation.

Still another object of my invention is to provide novel thread cutting apparatus which when actuated, automatically positions the sewing machine needle in an up position to thereby expose the needle thread for cutting.

Another object of my invention is to provide novel thread cutting apparatus including means for insuring that the thread cutting operation does not unthread the needle of the sewing machine.

The foregoing and other objects of my invention will become apparent from a careful reading of the following specification when taken in conjunction with the appended drawings, wherein:

FIGURE 1 is a fragmentary elevational view, partly in section, showing the Working end of a sewing machine head as seen looking into the front of the presser foot, and illustrates one view of the thread cutting hot wire system andthe auxiliary means employed to provide thread tension release in order to avoid rethreading of the needle` after a thread cutting operation;

FIGURE 2 is an end elevational View, also partly in section, of the sewing` machine head illustrated in FIGURE l, and illustrates certain organization details not visible in the latter figure;

FIGURE- 3 is a view of the presser foot as seen when viewed along the lines 3 3 of FIGURE 2;

FIGURE 4 is a sectional view through the presser foot seen in FIGURE 3 as viewed along the lines 4 4 of that figure; p

FIGURE 5 is an'underside view of the sewing machine throat, plate as seen when viewed from below along the lines 5-5 of FIGURE l;

FIGURE 6 is an enlarged fragmentary view of that section of the`throat plate of FIGURE 5 which is enclosed in the phantom circle;

FIGURE 7 is a sectional view through the throat plate of FIGURE 5 as seen when viewed along the lines 7--7 of FIGURE 6;

FIGURE 8 is a side sectional view taken through the presser foot as seen when viewed along the lines 8 8 of FIGURE 1 and illustrates the needle and bobbin threads in thread cutting position;

FIGURE 9 is aV fragmentary view as seen when looking down from above along the lines 9 9 of FIGURE 2 and illustrates the position change f the auxiliary thread puller arm when energized and deenergized;

FIGURES 10 through 16 illustrate in schematic form the electrical'circuitry associated with the thread trimming device, successive ones of these iigures illustrating successive phases of the thread cutting operation; I FIGURE l7`is avtiming diagram which shows in pictorial-form thesequence of and actuation duration of the various switched circuits embodied in the apparatus of FIGURES 10 through 16.

In these :several figures, like elements are denoted by like reference numerals.

Turning iirst to an examination of FIGURES 1 and 2 there is seen a conventional sewing machine head having the

usual thread lguides

31, and 37, a thread eyelet 36, a thread tensioner 32, slack thread regulator 33, thread take up lever 34, thread retainer 38, reciprocable needle bar 21k and needle 22 and` presser foot assembly 25. The presser foot assembly 25 includes a vertically shiftable presser foot shaft 26 operated by the presser foot lever 27, the presser foot 29 and supporting presser foot shank 28 being secured to the presser foot shaft 26 by a set screw 24. Immediately underlying the lowered presser foot 29 are two plies of

fabric

57 and 58 which have been partially stitched, these fabric plies being rmly pressed downward upon the throat plate 51 by the presser foot. The needle 22 is shown in its raised position,

Y which is the position occupied when a thread cutting operation is to be performed.

Underlying the needle hole 52 in the throat plate 51 is seen a bobbin 55 from which extends upwardly into Ythe partly stitched fabric plies the bobbin thread 56.

The needle thread 3tlis seen to be drawn from a thread supply and threaded through'the various thread guides, tensioner, and other'retainers, downward and through the eye of the needle 22. The foregoing sewing machine elementsA and their organization with respect to one another are seen to be completely conventional. However, certain other elements which appearin FIGURES l and 2, and which have not as yet been described repre-sent auxiliary attachments to the sewing machine, and in some cases modification of otherwise standard parts, and it is with these components that this invention is primarily concerned and to which attention should be primarily directed. Various aspects of these components are illustrated in FIGURES 3 through 9 in enlarged form for clarity and ease of understanding. Generally, insof far las the modificationsvwhich appear in FIGURES 1 and 2 are concerned, the new elements are seen to be the auxiliary thread pullers 40 and 60,`and the modiiica tions to standard parts are seen to reside in the inclusion of the hot wire elements into the presser foot 29 and throat plate 51. Y Y f Before describing the organizational cooperation Aamongst all of the elements in carrying out the thread trimming operation, it will be most conductive to a complete understanding of the invention kto first examine the modifications made to the presser foot 29 -as best seen in the showings of FIGURES 3 and 4, and the moditication made to the throat plate 51 as best seen in the showings of FIGURES 5, 6 and 7. Considering first the modified presser foot 29 illustrated in FIGURES 3 and 4,V it is seen that a horizontally transversely extending hole has been drilled through the forwardly extending toes 85 of the presser foot 29, and a` wire 80 inserted through the hole and extending outwardly to either side of the presser foot 29.V The wire 80, which may be made for example of Chromel wire, is bound in a central position within the hole by a bonding agent 84, which may i be for example a high temperature thermosetting epoxy res1n.

The epoxy resin bonding agent 84 serves to insulate the Chromel wire 80 from the body of the presser foot 29, and hence prevents the Chromel wire 80 from being electrically short circuited by the presser foot, this latter condition being undesirable for tworreasons. Firstly, short circuiting of the Chromel wire 80 by the presser foot 29 would effectively prevent any substantial electrical energizing current from being passed through the Chromel wire, with the attendant consequence that the wire would not be heated and would therefore be rendered inoperative for severing the needleA thread. Secondly, the epoxy resin 84 provides a substantial heat barrier between the Chromel wire and the presser foot 29, without which, the presser foot 29 would act as a heat sink and rapidly conduct away the heat developed in the Chromel wire 80 when the latter is electrically energized for thread cutting. In this case, also, the Chromel wireV 80 could be rendered inoperative for its purpose. The characteristics required for the bonding agent S4 are therefore that it be a good electrical insulating agent, a reasonable heat barrier, and it must not itself be susceptible to break down as a result of the relatively high temperatures developed in the Chromel wire 841, which may be as high as 700 F.

Butt welded or otherwise connected to the ends of the Chromel wire Sti are a pair of copper leads 81, which are in turn each respectively connected to one of the energizing

electrical conductors

82 and 83, the latter being seen in the showings of FIGURES 1 and 2. The manner in which the

conductors

82 and 83 are energized will be fully described in connection with the showings of FIGURES 10 through 16 subsequently to be described. The relative position of the Chromel wire 80 in the presser foot 29 with regard to the sewing machine needle 22 is best illustrated in the showing of FIGURE 8 where it can be seen that the Chromel Wire 80 is located substantially to the rear of the needle hole 52 in the throat plate 51, and hence is positioned to the rear of the needle 22, so that during normal stitching operations the Chromel wire 80 does not interfere with the reciprocating motion of the sewing machine needle 22.

Turning now to the showings of FIGURES 5, 6 and 7 illustrating the modiiied throat plate 51, it is seen that a channel has been cut into the undersurface of the throat plate extending from some convenient point on the edge thereof inwardly to encompass the needle hole 52. Within this channel is disposed a second Chromel Wire 7@ which loops around the needle hole 52 and eX- tends outwardly toward the edge of the throat plate 51, being butt welded at its ends to a pair of copper leads '771. The Chromel wire '7d and copper leads '71 are secured within the channel by a bonding agent 74 which may be Van epoxy resin of the same type andremployed for the same purposes as the bonding agent 84 already described in connection with the showing of FIGURES 3 and 4.

As best seen in the showing of FIGURE 7 the Chromel wire 76 is not ycompletely surrounded by the bonding agent 74, but is rather secured to the throat plate 51 with a free surface portion which may be brought into v contact with the bobbin thread 56 in order to sever the latter. The copper leads 71 are each connected in turn to one of a pair of

conductors

72 and 73 which conduct the electrical energizing current to the Chromel wire during the thread cutting operation. The throat plate 51 is provided in the normal manner with feed dog slots 53, as seen in FIGURE 5, but it will be observed that the Chromel wire 70 extends Ytransversely of the righthand most slot. In order that the feed dogs which ellip` tically oscillate in these -slots 53 to advance the fabric under the needle 22 should not cut through the Chromel wire 70 and thereby destroy Vthe circuit continuity to the energizing source, the feed dogwhich oscillates in the right-hand most slot 53 is recessed downwardly by cutting out several of the teeth thereon to thereby insure clearance between the oscillating feed dog and the Chromel wire 70.

Understanding now that the thread trimming or cutting oper-ation is to be carried out by heating the

Chromel wires

70 and 80 bonded into the throat plate 51 and presser foot 29 respectively and then laying the needle thread 3l) and bobbin thread 56 thereagainst in order to burn through and sever these threads, it will be appreciated from the showings of FIGURES 2 and 8 that during some portions of the normaloperation of the sewing machine th-at needle thread 30 and the bobbin thread 56 do not engage the

Chromel wires

70 and 80, and hence some means must be provided to insure that the bobbin and needle threads are positively pressed against these wires when it is desired to sever them during a thread trimming operation.

Moreover, if the needle thread 30 were severed while under normal tension maintained during a stitching operation, the needle thread 30 would snap back through the eye of the needle 22 and hence require that the needle be rethreaded before stitching could be resumed. It is the specific function of the auxiliary thread puller 40 mounted to the sewing machine head near the thread tensioner 32 to provide a certain amount of slack in the needle thread 3@ so that the needle 22 is not unthreaded when a thread trimming operation is carried out. The function of the auxiliary thread puller 60 mounted below the throat plate 51 and adjacent the bobbin 55 is to displace the bobbing thread 56 from its central position in the needle hole 52 of the throat plate and to shift this bobbin thread laterally and generally rearwardly into positive engagement with the Chromel wire 70 which trims the needle hole 52.

Examining now FIGURES l and 2 for details of the auxiliary` thread pullers `40 and '66, it is seen that the auxiliary thread puller 4t) includes a loop-ended arm 45 secured to a sleeve 43 by a machine Screw 46, and that the sleeve 43 is secured to the shaft 42 of a rotary solenoid 41 by a machine screw 44. The rotary solenoid 41 is affixed to a bracket 47 which is in turn secured to the sewing machine head by a pair of screws 59. The rotary solenoid 41, when energized via the

conductors

49 and 50 causes the solenoid shaft 42 to rotate and carry the arm 45 outward away from the sewing machine head 2G. The needle thread 30, which is passed through the loop on the end of the arm 45 when the machine is first threaded, is carried outward with the arm 45. Since the needle thread 30 cannot be back pulled out of the stitched fabric plies 57 and 58, the pull exerted on the needle thread 30 by the rotation of the arm 45 causes thread to be pulled from the thread supply through the thread tensioner 32. Hence, when the arm 45 returns to its position as illustrated in FIGURE 2 upon deenergization of the rotary solenoid 41, a predetermined amount of slack results in the needle thread 30 which relieves the tension therein sufficiently to prevent unthreading of the needle 22 upon severance of the needle thread 30 by the Chromel wire 80.

The auxiliary thread puller 6! associated with the bobbin thread 56 is similar in construction and operation to the auxiliary thread puller 40 and is so positioned relative to the bobbin thread 56 and needle hole 52 of the throat plate 51 that rotation of the arm 61 pulls a predetermined amount of thread outwardly from the bobbin 55 and causes the bobbin thread 56 to be laid over firmly against the exposed surface of the Chromel wire 70 in the throat plate 51. FIGURE 9 illustrates exemplary positions of the arm 45` of the auxiliary thread puller 40 when deenergized and whcnenergized, the solid line construction illustrating the` normal or deenergized state of the rotary solenoid 41 and the broken line showing the displaced position of the arm 45 when the rotary solenoid 41 is energized. The identical action takes place, of

course, with regard to the arm 61 of the rotary solenoid incorporated into the auxiliary thread puller 60, energization of this solenoid being by means of the

conductors

62 and 63. 1

The one remaining point to be considered before turning to an examination of FIGURES 10 through 17 for an understanding of the operational sequence which takes place when a thread cutting operation is initiated, is the means by which the needle thread 30 which normally lies in advance of the Chromel wire in the presser foot 29 is shifted rearwardly into trimming position against the Chromel wire. Since in order to cut the needle thread 30, it is necessary that the needle 22 be raised to expose the thread, advantage is taken of the fact that the fabric being stitched is advanced through the sewing machine a distance equal to one-half stitch when the needle 22 is shifted from its down to its up position.

The half step fabric advance is accomplished by the motion of the feed dogs which grip the under side of the fabric .through the feed dog slots 53 in the throat plate 51. One of the feed dogs 54 is shown in representational form in the showing of FIGURE 8 where it is likewise seen that the half stitch fabric advance displaces the needle thread 3() rearwardly a suiiicient dist-ance to bring it into engagement with the Chromel wire S0, and wherein 4likewise it may be seen that the bobbin thread 56 has been similarly shifted rearwardly by the arm 61 of the auxiliary thread puller 6) so that it firmly engages the exposed surface of the Chromel wire 70 embedded in the underside f-o the throat plate 51.

In summary, the general sequence of events will be as follows. First, the sewing machine must be stopped with the needle 22 in raised position to expose the needle thread 30 and advance the fabric one-half stitch rearward to properly position the needle thread 30 and bobbin thread 56. Then the thread trimming operation proper is initiated which includes the energization of the auxiliary thread pullers 40 and 60 to respectively provide a slack action in the needle thread 30 and a positive engagement action of the bobbin thread 56 with the Chromel wire 70. Finally, the

Chromel wires

70 and 80 are energized sufficiently to burn through the needle thread 30 and bobbin thread 56 to complete the thread trimming operation. Understanding now the general manner in which the thread cutting operation is to be carried out according to the invention, attention should be directed to the showings of FIGURES l0 through 17 where conttrol apparatus for selectively energizing the rotary solenoids and the thread cutting Chromel wires in a particular timed sequence is illustrated in detail.

Examining irst FIGURE 10, there is seen a transformer 96 `having a primary winding 91 connected to a source of alternating current by the

conductors

113 and 114, and having three independent

secondary windings

92, 93 and 94. The secondary winding 92 is connected .to a pair of crystal rectiiiers 95 in a full-wave rectifying circuit, the rectified voltage therefrom being applied to the solenoid coil 64 of the auxiliary thread puller 6i) by the

conductors

63 and 62 through the switch 108- when the latter is closed. Similarly, the rectified output of the full-wave circuit including the secondary winding 93 and the crystal rectifiers 96 is applied to the solenoid coil 48 -of the auxiliary thread puller 40 via the

conductors

49 and 50 through t e switch 107 when the latter is closed.

One end of the secondary winding 94 is connectedvia a conductor 111 to the movable contacts 66 4and 68 of a pair of

rheostats

65 and 67 respectively, while the other end of the winding 94 is connected to the junction of the

conductors

72 and 82 associated with the

Chromel wires

70 and 30 via the conductor 110 and the switch 109 when the latter is closed. Theconductors 73 and 83 associated respectively with the

Chromel wires

70 and 80 connect to one end of the

rheostats

65 and 67 respectively, thus forming a continuous electrical circuit when the switch 169 is in its closed position. The

rheostats

65 and 67 are seen to be respectively series connected Vwith the Chromel wires '70 and 80 and are therefore effective to control the magnitude of the currentthrough lthese wires between limits established by the maximum and minimum settings of the rheostat movable contacts'd and 68.

In general the

rheostats

65 and 67 would be available to the sewing machine openator as setable controls. The machine operator is thereby enabled to set these rheostats to provide the necessary amount of heating current to sever diierent kinds Vof threads, as for example, a iirst setting for cotton threads and a different setting for nylon threads. The Various setting of the rheostats once determined may be marked on a suitable escutcheon plate positioned behind the control knob for each of the rheolstats movable contacts so that rapid resetability to desired contact positions in easily achieved.

The

switches

107, 198 and 109 are shown in their normally open condition and are only closed in response to a closing pressure exerted thereon by the cams 103, 1&4 Aand 165 respectively of the timer 10@ when cam mot-ion is initiated and maintained by the energization of the winding 1ll1`of the timer motor. The remaining cam 1112 yof the timer i) actuates the holding switch 1% to maintain the timing motor winding 1tl1energized during the thread cutting cycle of operation, and to energize and stop the timer at the completion of the operation. The timer motor winding 1111 is energized from the same source of alternating current which energizes the primary Winding of. the transformer 90, such winding energization being switch controlled.

The current flow path through the ywinding 161 may be traced from one terminal of the alternating current source to the lower end of the winding 1111 via the

conductors

113 and 112, through the Winding 101 and from the top of the winding to the pole of the switch 106 via the conductor 119. the switch 1116'is returned to the other side ofthe alternating current source via the conductor'115, the latter being connected'to the lower contact of the switch 122. The right-hand contactof the switch 1115 connects via the conductor-116m the'pole of the .switch 122 -through the normally` open switch 123. Thus, to energize the timer motor, the pole of'the switch 122 is transferred from its normally open upper contact to the lower contact, which Y then closes 4the electrical circuit from the source of alternating current through the Winding 10.1 ofthe timer motor. Ganged to the pole of the switch .122 is the pole of a second switch 121 which is shown in a normally open condition, the pole of the switch 4121 being connected to one conductor 117 of -an external circuit (not shown), and the lower contact of the switch 121 being also connected to the same external circuit via the conductor 118. The

The normally open left-hand contact of two

switches

121 and 122 aretherefore ganged together l for simultaneous actuat-ion and may optionally be com. bined into one double-pole single-throw switch. VThe `switches 121 and-122 a-re operator actuated and in fact are the switches which initiate the thread cutting operation. i

Recall-ing now from the earlier description that the sewing machine needle 22 must be in its raised position when a thread cutting operation is initiated, it is clear that it wouldfbe highly desirable to relieve the operator yfrom the `burden of turning lthe balance wheel by hand to raise the needlewhen he wishes to trim the needle and bobbin threads. The switch 121 is provided to accomplish the automatic needle raising simultaneously with the initiation ofl the thread -cutting operation provided that the sewing machine is already equipped with an automatic needle positioning mechanism such as is described in my application entitled Automatic Needle Positioning Mechanism, assigned'to t-he same assignee as the instant application, nowv matured as United States Patent No. 2,961,591, dated November 22, 1960.` In this regard, the switch 121 when actuated by. theV operator, performs the sam'efunction as the knee-lift switch 1119 in FIGURE l0 d of my copending application by completing a circuit between the conductors 111i and 1-11 as shown therein,

Returning now to FIGURE l0 of the instant application, the normally open switch ,123 shown therein is provided to insure that the timing motor winding 1111 may not be energized unless the sewing machine has been stopped. The switch 123 may be incorporated into the sewing machine treadle mechanism in such a way that it is opened when the treadle is depressed to operate the sewing machine and closes when the treadle is released and the sewing machine is therefore broughtto a stop. The inclusion of the switch 1123 is of course optional and may 4be dispensed with if desired. In FIGURES 11 through 16 which follow, the switch123 would normally be closed and it is therefore not included in these showings.

The timing diagram of FIGURE l7 illustrates the closure conditions for the

switches

106, 107, 108 and 1119 relative to one another during the thread cutting operation, and the duration of the conditions pictured in each of the sequence diagrams of FGURES 1l through 16 are correlated into the timing diagram of FIGURE 17. In the following description of FGURES ll through 16 reference should be simultaneously made to FIGURE. 17.

Turning now to the conditions` as illustrated in the showing of FIGURE l1, it will be assumed that the sewing machine has come to a stop and that the operator ha-s actuated the ganged switches .121 and 122. The

switches

121 and 122 are preferably of the momentary-make type and do not require to be held closed by the Voperator or by any locking type device. The actuation of the switches i121 and 122 causes the sewing machine needle to rise by actuation of the automatic needle positioning mechanism previously mentioned, `and closes a circuit from a source `of alternating current `through theY winding 1111 of the timer motor. The current flow circuit through the time-r motor winding 1111 is shown in -heavy line in FIGURE ll and may be traced from the source of alternating current down through the conductor 115 and 4over to the righthand contact of the switch 1126 via the now closed switch A122 and conductor 116. :From the switch 1616 the current flows via conductor 119 to the top of the timer motor winding 1111, down through the winding and back to the yother terminal of ythe source of alternating current via the conductor 112.

Energization of the timer motor causes the motor shaft to rotate carrying with it the cams 1112, 1623, 1114 and 165. None of the switches 1116 through 109 are actuated for approximately titty milliseconds after initiation yof the thread cutting operation as may be seen from the timing diagram `of FIGURE 17. The fifty millisecond interval insures that ample time is provided to allow the sewing machine needle to rise to its upper position. At the end yof this time, the cam 1012 has rotated sufficiently to cause the pole of the switch 166 to transfer from its right-hand contact to its left-hand contact, .as will be seen in FIG- URE l2, and thereby establish the current flow path y through the timer motor winding 101-to the conductor 115 by bypassing the conductor 116 and switch 122.

When the momentary-make swi-tch `122 now opens (as also seen in FIGURE l2) the energization ottimer motor winding 1111 is not interrupted but is maintained througr the holding circuit established by the transfer of the pole of thev switch 166. The timer mo-tor continues to run :and rotate the shaft to which the cams 162 through 1115 are aiiixed for approximately two seconds after the pole `of the switch 122 transfers, and during the first one-hundred and titty milliseconds of this time none ofthe switches y167, 1113 or 1119 are closed. Consequently, the rotary solenoid coils 418 and e4 remain deenergized and no energizing current is delivered to the Chrome] wires 711 and Sil.

FIGURE l2 illustrates the `conditions after the lapse of approximately one-hundred and fifty milliseconds from the initiation of the thread cuttingv operation by closure of Vthe switches 121and 122. At this time cams 103 and 194 respectively close the switches 167 and 1118V to energize the rotary solenoid coils 48 and 64. The auxiliary thread pullers 40 and 60 are therefore energized and the

arms

45 and 61 are displaced in the manner and for the purposes previously described. The cam 105 has, however, not rotated into such position as will close the switch 109 and hence the

Chromel wires

70 and 80 remain deenergized. The conditions of FIGURE 12 are maintained for approximately one-hundred and fifty milliseconds, at the end of which time the cam 103 of the timer 100 causes the switch 107 to open and thus deenergize the solenoid coil 48 of the auxiliary thread puller 40 associated with the needle thread.

The conditions obtaining for the next fifty milliseconds are seen in the showing of FIGURE 13 where it is observed that the solenoid coil 64 of the auxiliary thread puller 60 remains energized through switch 108 and thereby holds the bobbin thread 56 over against the Chromel wire 70 in the throat plate 51. The bobbin thread 56 is thus prepared for severance when the Chromel wire 70 is subsequently energized, and the needle thread 30 has experienced a substantial reduction in tension to prevent unthreading of the needle 22 upon the subsequent energization of the Chromel wire 80.

At the end of the fifty millisecond time interval during which the conditions of FIGURE 13 hold, the cam 105 of the timer 100 closes the switch 109 as seen in FIGURE 14 and thereby energizes the

Chromel wires

70 and 80 from the transformer secondary winding 94 via the conductors 110, 111 and the

rheostats

65 and 67. Cam 104 of the timer 100, of course, continues to hold the switch 108 in its closed condition to thereby maintain the solenoid coil 64 of the auxiliary thread puller 60 in its energized condition and keep the bobbin thread 56 firmly over against the Chromel wire 70. The conditions of FIG- URE 14 continue for approximately fiftymilliseconds, at the end of which time cam 105 of the timer 100 allows the switch 109 to open and thus deenergize the

Chromel wires

70 and 80, fifty milliseconds having been found to be a sufficient length of time to cause severance of varying kinds of needle and bobbin threads.

Upon the opening of the switch 109, the conditions as illustrated in FIGURE 14 are altered to thoseas seen in the showing of FIGURE 15 wherein it is seen that the timer continues to run by virtue of the energization of the winding 101 of the timer motor through the holding circuit of switch 106, and that the solenoid coil 64 of the auxiliaryv thread puller 60 continues in its energized state. The conditions of FIGURE 15 are maintained for approximately one-hundred milliseconds, at the end of which time the cam 104 of the timer 100 allows the switch 108Y to open and thus deenergize the solenoid coil 64 of the auxiliary thread puller 60 and establish the conditions as now seen to hold in the showing of FIGURE 16.

The entire operation up to 'this point occupies a time interval of approximately ve-hundred milliseconds, as may be seen in the showing of the timing diagram of FIG- URE 17, and the timing motor continues to run for an additional fifteen-hundred milliseconds during which time only the switch 106 remains actuated by its associated cam 102. At the end of this total two second time interval commencing with the initiation of the thread cutting operation, the came 102 Aof the timer 100 allows the 'switch 106 to transfer its pole from the left-hand contact over to the light-hand contact and thus break the holding circuit for the motor winding 101. The timer motor therefore stops and the conditions portrayed inthe showing of FIGURE are again established. l i 1 It may be found desirable in some instances to establish a safety interlock arrangement whereby the transfer of the pole of switch 106 to establish the holding current circuit for the timer motor Winding causes the sewing machine to be rendered inoperable until the thread cutting operation has been terminated. Although, not shown, such an interlock is very easily incorporated into the thread cutting apparatus by for example .providing the switch` 106 with a second pole and associated normally open contact. This second pole end associated normally open contact may be connected in series with a source of energizing current and a solenoid coil the solenoid when energized actuating a plunger or other latching mechanism to lock the sewing machine treadle and thereby prevent operation of the sewing machine stitching mechanism during the thread trimming operation. At the end of the thread trimming operation when the switch 106 is restored to its normal position, the second pole thereof would of course break open from engagement with its associated contact and thereby deenergize the solenoid coil to unlock the treadle.

Having now described my invention in connection with the particular embodiment illustrated in the appended drawings, many modifications and variations of my invention will naturally suggest themselves to those persons normally skilled in the art without departing from the essential spirit or scope of my invention, and accordingly it is intended to claim the same broadly as Well as specifically as indicated by the appended claims.

What is claimed as new and useful is:

1. In combination with a sewing machine, a thread trimming device for severing the needle thread of the sewing machine comprising, an electrically energizable heat generating element, shiftable sewing machine presser foot means for supporting said element in operative position in closely spaced relationship to the upper surface of an article being stitched, energizing means effective when actuated to couple said element to a source of electrical energization, control means coupled to said energizing means and under the control of the sewing machine operator for selectively actuating said energizing means, and means for shifting the needle thread against said heat generating'element when said shiftable presser foot is in a first selected position, whereby, when -said shiftable presser foot is in said first selected position, when the needle thread is in engagement with said heat generating element, and when said control means is actuated, said element is energized and rendered effective to burn through the needle thread.

2. The thread trimming device according to claim 1 wherein said sewing machine includes a reciprocating needle having an eye therein for receiving the needle thread and further includes needle thread tension reducing means actuatable by the sewing machine operator and effective when actuated to reduce the needle thread tension prior to severance of the needle thread by said heat generating element, whereby said needle thread when severed does not snap back through the needle eye and unthread the needle.

3. The thread trimming device according to claim 1 wherein said presser foot means includes a presser foot having laterally spaced toe portions and said electrically energizable heat generating element is a resistance wire having a portion thereof extending freely within the space between the toe portions of the presser foot and proximate to the axis of reciprocation of the sewing machine needle.

4. A thread trimming device for severing the needle thread of a sewing machine comprising in combination, a shiftable sewing machine presser foot having laterally spaced toe portions including an electrically energizable heat generating resistance wire disposed within a transversely extending hole passing through the toe portions of the presser foot, said resistance wire being physically fixed within said presser foot hole and electrically insulated from said presser foot by a bonding agent having the ability to withstand without breakdown the maximum temperature developed in said resistance wire, first means effective when actuated to couple said resistance wire to a source of electrical energization, second means coupled to said first means and under the control of the sewing machine operator for selectively actuating said first means, and third means for shifting the needle thread against said resistance wire during at least a portion of the normal repetitive reciprocation cycle of the needle when said presser foot is seated down against the upper surface of is down, when the needle thread is in engagement with said resistance wire, and when said second means is actuated by the sewing machine operator, said resistance wire is energized and rendered effective to burn through the needle thread.

5. A thread trimming device for severing the needle thread of a sewing machine, comprising in combination,

within said presser foot so that the sewing machine needle passesVV in frontV thereof during vertical reciprocation of the needle during a stitching operation, first means effective when actuated to couple -said resistance wire to a source of electrical energization, second means coupled to said iirst meansand under the control of the sewing machine operator for selectively actuating said first means, and third means ,for shifting the needle thread against said resistance wire during at least a portion of the normal repetitive reciprocation cycle of the needle when said presser foot is seated down against the upper surface of an article being stitched, whereby, when said presser foot is down, when the needle thread is in engagement with said resistance wire, and when said second means lis actuated by the sewing machine operator, said resistance wire isl energized and rendered effective to burn through the needle thread.

6. A thread trimming device for -severing the needle .thread of a sewing machine having a needle thread tensioningdevice and a reciprocating needle with an eye therethrough for receiving the needle thread comprising, an electrically energizable heat generating element, rst presser foot means for supporting said element in closely spaced relationship to the upper surface of an article being stitched, secondmeans eiective when actuated to couple said element to a source of electrical energization, third means coupled to said second means and under the control ofV the'sewing machine operator for selectively actuating said second means, fourth means for shifting the needlethread against said heat generatingelement during at leastva portion of the normal repetitive reciprocation cycle of the needle when said shiftable supporting means is in a irst selected position, and needle thread tension reducing means actuatable by the sewing machine operator and effective when actuated to reduce the needle thread tension prioryto severance of the needle thread by said heat generating element, said needle thread tension reducing means'comprising a loop-ended swingable arm with the needleV thread passing through the loop in said arm, said varm loop being located betweenk the needle and said sewing machine needle thread tensioning device along the course -of the needle thread, saidtension reducing means further including electrically energizable fifth means coupledto said swingable arm and effective when energized to swing said arm and draw thread-from the needle thread supply through said sewing machine needle thread tensioning device so that the needle thread tension is reduced below that normally obtaining, and sixth means effective when actuated for coupling 4said fifth means to a source of energization, whereby, whensaid shiftable supporting means is inV said irst selected position, when the needle thread is in engagement with said heat generating element, and when said third'and sixth'rneans'are actuated, said element is energized and rendered effective to burn through the needle thread and said needle thread when'severed does not snap back through theV needle eye and unthread the needle. Y

7. A thread trimmingdevice for severing the needle thread of a sewing machine having a reciprocating needle with an eye therethrough forreceiving a needle thread, comprising, an electrically energizable heat generating element, presser foot means for supporting saidelement in closely spaced relationship to the upper surface of an article-being stitched, lirst actuating-means elective when operated to couple said element to a source of electrical energization, means for shifting the needle thread against said heat generating element when said presser foot means is down, and needle thread tension reducing means actuatable by the sewing machine operator and elective when actuated to reduce the needle thread tension prior to severance of the needle thread by said heat generating element, said needle thread tension reducing means including a swingable arm and electrically energizable means coupled to said swingable arm and effective when energized to swing said arm and reduce the needle thread tension below that normally obtaining, second actuating means eiective when operated for coupling said electrically energizable thread tension reducing means to a source of energization, and control means under the control ofvthe operator for operating said first and second actuating means whereby, when said presser foot means is down, when the needle thread is in engagement with said heat generating element and when said control means is operated, said element is energized and rendered effective to burn through the needle thread and said needle thread when severed Vdoes not snap back through the needleeye and unthread the needle.

8. The thread trimming device according to claim 6 whereinv said third means is also coupled to said sixth means and controls theV actuation thereof, said third means actuating said sixth and second means in a predetermined sequence and for predetermined time intervals.

9. The thread trimming device according to claim 8 wherein said second and sixth means each include a switch which when closed completesan electrical circuit between the source of energization and said heat generating element and electrically energizable fth means respectively, `and wherein said third means includes a plurality of motor driven. rotatable cam elements, a tirst one of said cam elements being efective during a part of its rotation cycle to close the second means switch, and a different one of said'cam elements being. etective during part of its rotation cycle to close the sixth means switch, each cam element beingy soshaped relative to the other and so positioned relative to its associated switch that said switches are closed. in the said predetermined sequence as said cams rotate. f

10. The thread trimming device according to claim 7 wherein said rst and second actuating means each include a switch which when closed completes an electrical ,circuit between the source of energization and said heat generating element and electrically energizable thread tension reducing means respectively, and wherein said control means includes a plurality of motor driven rotatable cam elements, a first one of said cam elements being effective duringV a part of its rotation cycle to close the iirst'actuating means switch, and a different one of said cam elements being eifective during part of its rotation cycle to close the second actuating means switch, each cam element being so shaped relative to the lother and so positioned relative to its associated switch that said switches are closed in a predetermined sequence and for predetermined time intervals as said cams rotate.

11. A thread trimming device for severing the bobbin thread of asewing machine, comprising in combination, an electrically energizable heat generating resistance wire, a sewing machine throat plate having a needle hole eX- tending therethrough and carrying said resistance wire in closelyspaced relationship to the under surface of an article being stitched with the resistance wire disposed in 'substantially encircling relationship to the needle hole inf the throat plate, rst means effective when actuated to vcouple said element to a source of electrical energization, asecond means effective when energized for shifting the bobbin thread intoY positive engagement with said heat'generating element,'third means effective when actuated for coupling said second means to a source of energization, and `fourth means under the control of the sewing machine operator for selectively actuating said first and third means, whereby, when said fourth means is operated said heat generating element is energized and the bobbin thread is shifted into positive engagement therewtih.

12. The thread trimming device according to claim 11 wherein said resistance wire is physically fixed to said throat plate by a bonding agent electrically insulating said wire from said throat plate, being a good heat barrier, and having the ability to withstand without breakdown the maximum temperature developed in said resistance wire. i

13. A thread trimming device for severing the bobbin thread of a sewing machine having a throat plate with a needle hole extending therethrough comprising, an electrically energizable heat generating element, first means for supporting said element in closely spaced relationship to the under surface of an article being stitched, second means effective when actuated to couple said element to a source of electrical energization, third means effective when energized for shifting the bobbin thread into positive engagement with said heat generating element, fourth means effective when actuated-for coupling said third means toa source of energization, and fifth means under the control of the sewing machine operator for selectively actuating said second and fourth means, whereby, when said fifth means is operated said heat generating element is energized and the bobbin thread is shifted into posi` tive engagement therewith, said third means comprising a loop-ended swingable arm with the bobbin thread passing through the loop in said arm, said arm loop being located along the course of the bobbin thread between the bobbin and the throat plate needle hole, said third means further including electrically energizable sixth means coupled to said swingable arm and effective when energized to swing said arm and shift the bobbin thread into positive engagement with said heat generating element.`

`14. The thread trimming device according to claim 13 wherein said second and fourth means each include a switch which when closed completes an electrical circuit between the source of energization and said heat generating element and electrically energizable sixth means respectively, and wherein said fifth means includes a plurality of rotatable cam elements, a first one of said cam elements being effective during a part of its rotation cycle to close the second means switch, and a different one of said cam elementsbeing effective during part of its rotation cycle to close the fourth means switch, each cam ele-` ment being so shaped relative to the other and so positioned relative to its associatedA switch that said switches are closed in a predetermined sequence and for predetermined time intervals as said cams rotate.

15. A thread trimming device for severing the bobbin thread of a sewing machine, comprising in combination, an electrically energizable heat generating resistance wire, a sewing machine throat plate having a needle hole eX- tending therethrough and carrying said resistance wire in closely spaced relationship to the under surface of an article being stitched with the resistance wire disposed adjacent to the needle hole in the throat plate, first actuating means effective when actuated to couplesaid element to a source of electrical energization, means effective when energized for shifting the bobbin thread into positive engagement with said heat generating element, second actuating means effective when actuated for coupling said thread shifting means to a source of energization, and control means under the control of the sewing machine operator for selectively actuating said first and second means, whereby, when said control means is operated said heat generating element is energized and the bobbin thread is shifted into positive engagement therewith, said first and second actuating'means each including a switch which when closed completes` an electrical circuit between the source of energization and said lheat generating element and electrically Venergizable thread shifting means respectively, and said control means including a plurality of rotatable cam elements, a first one.

' and a different one of said cam elements being effective during part of its rotation cycle to close the second actuating means switch, each cam element being so shaped relative to the other and so positioned relative to its associated switch that said switches are closed in a predetermined sequence and for predetermined time intervals as said cams rotate.k

16. The thread trimming device according to claim 14 wherein said fifth means further includes an electrically energizable motor effective when energized to rotate the aforesaid plurality of rotatable cam elements, said cam elements being coupled to the motor shaft for rotation therewith, an operator actuatable switch effective when actuated to start said motor by connecting the motor energizing winding to a source of electrical energization, and a switch closable by one of said plurality of rotatable cams for establishing a holding current circuit between said motor winding and source of electrical energization in the time interval during which said operator actuatable switch is actuated, the cam which closes ythe holding current circuit switch being so shaped that said switch is held closed` for a time interval substantially equal to the duration of the thread trimming operation and then causes said switch to open to deenergize said motor and terminate the thread trimming operation.

, 17. The thread trimming device according to claim 15 wherein said control means further includes an electrically energizable motor effective when energized to rotate the aforesaid plurality of rotatable cam elements, said cam elements being coupled to the motor shaft for rotation therewith, an operator actuatable switch effective when actuated to start said motor by connecting the motor energizing winding to a source of electrical energization, and

a switch closable by one of said plurality of rotatable cams for establishing a holding current circuit between said motor winding and source of electrical energization in the time interval during which said operator actuatable switch is actuated, the cam which closes the holding current circuit switch being so shaped that said switch is held closed for a time interval substantially equal to the duration of the thread trimming operation and then causes said switch to open to deenergize said motor and terminate the thread trimming operation.

18. The thread trimming device according to claim 16 further including means in series with said operator actuatable switch for rendering the latter inoperative to start said motor when the sewing machine drive mechanism is operating.

19. The thread trimming device according to claim 16 comprising further means including a switch ganged to said holding current circuit switch and operable therewith for rendering the sewing machine inoperable during the thread trimming operation by actuating a device which locks the sewing machine treadle to thereby prevent operation of the same by the sewing machine operator.

20. A thread trimming device for severing the needle thread of a sewing machine comprising, an electrically energizable heat generating element, first shiftable means for supporting said element in closely spaced relationship to the upper surface of an arti fe being stitched, second means effective when actuated to couple said element to a source of electrical energization, third means coupled to said second means and under the control of the sewing machine operator for selectively actuating said second means, and fourth means for shifting the needle thread against said heat generating element during at least a portion of the normal repetitive reciprocation cycle of the needle when said shiftable supporting means is in a first selected position, said fourth means comprising sewing machine feed dogs which advance the fabric being stitched for a distance equal to one half stitch as the sewing machine needle moves from its down to its up position so that the needle thread extending upward from the fabric is shifted rearward against the electrically energizableiheat generatingelement, whereby, when said shiftable supporting means is in said first selected position, when the needle thread is in engagement with said heat generating element, and when said third means is actuated, said element is energized and rendered effective to burn through the needle thread.

2l. A thread trimming device for severing the needle thread of a sewing machine, lcomprising in combination, an electrically energizable Vheat generating element, means for supporting said heat generating element in closely spaced relationship to the upper surface of an article being stitched, means for'shifting the needle thread against said heat generating Ielement when the latter is disposed as aforesaid closely above the article being stitched during at least a portion of the'normal repetitive reciprocation cycle of the needle, and means selectively operable under the control of the sewing machine operator effective when operated to couple said heat generating element to a source of electrical energization, whereby, when the needle thread is in engagement with said heat generating. element operation of said lastV named means renders said heat generating element effective'to burn' through said needle thread, said means for shifting the needle thread against said heat generating' elementpcomprising sewing machine feed dogs which advance the fabric being stitched for a distance equal to one half stitch as the sewingV machine needle moves from its down to its up position so'that the needle thread extending upward from the article being stitched isshifted rearward against the electrically energizable heat generating element.

22. A thread trimming device for` severing the needle thread of a sewing machine having a needle thread tensioning device and a reciprocating needle with an eye therethrough forreceiving the needle thread, comprising in combination, rvan electrically energizable heat generating element, means for supporting said heat generating element in closely spaced relationship to the upper surface of an article being stitched, means for shifting the needle thread against said heat generating element when the latter is disposed as aforesaid closely above the article being stitched during at least a portion of the normal repetitive reciprocation cycle of the needle, needle thread tension reducing means comprising a loop-ended swingable arm located between lthe needle and said sewing machine needle thread tensioning devicealong the course of the needlel thread with the needle thread passing through the loop in said arm, electrically energizable means coupled to said swingable arm and effective when energized to swing said arm and draw thread from the needle thread supply through said sewing machine needle thread tensioning device, and means selectively operable under the control of the sewing machine operator effective when operated to couple said heat generating element and said energizable needle thread arm swinging means to a source of electrical energization, whereby, when the vneedle thread is in engagement with said heat generating element oper-ation of said last named means is effective to reduce the needle thread tension prior to severance of the needle threadand renderV said heat generating element effective to burn through' said needle thread so that said needle thread when severed does not snap back through the needle eye and unthread the needle. Y .23. The apparatuses set forth in claim 1 further including,V a thread trimmingdevice for severing the bobbin thread of the sewing machine, comprising in combination, an electrically energizable heat generating resistance wire, a sewing machine throat plate having a needle hole eX- tending therethrough and carrying said resistancewire in closely spaced relationship to the under surface of an article being stitched with the resistance wire disposed adjacent Vto the needle hole in the throat plate, electrically energizable means effective when energized for shifting l@ the .bobbin threadV into positive engagement withsaid resistance wire, and means -selectively operable under the control of the sewing machine operator effective when operated to couple said resistance wire and said bobbin thread shifting means to a source'of electrical energization, whereby, upon operation of said last named means a loop-ended'swingable arm disposed so that the bobbinv thread passes through the loop in said arm, said arm loop being located along the course of the bobbin thread between the bobbin and the throat plate needle hole, electrically energizable means coupled to said swingable arm and effective when energized to swing saidarm Iand shift the vbobbin thread into positive engagement with said heat generating element, and means selectively operable under the control ofthe sewing machine operator effective when operated to couple said heat generating element and saidl arm swinging means to a source of electrical energization, whereby, upon operation of said last named kmeans said heat generating element is rendered effective to burn through the bobbin thread and the bobbin thread is shiftedV into positive engagement therewith.

25. The apparatus as set forth in claim 23 in which the sewing machine includes `a throat plate with a needle hole therethrough and a bobbin beneath the throat plate,

wherein, said bobbin thread shifting means comprises ka shiftable member located between the bobbin and the throat plate needle hole and disposed so that the bobbin thread passes therethrough.

26. The thread trimming device `according to claim 15 wherein said control 4means further includes an electrically energizable motor effective when energized to rotate the aforesaid plurality :of rotatable cam elements, said cam Y elements being coupled to the motor shaft for rotation therewith, an operator actuatable switch effective when actuated to start said motor by connecting the motor energizing winding to ya source of electrical energization, and

switch closable by one of said plurality of rotatable cams for establishing a holding current circuit between said motor winding and source of electrical energization in the time interval during which said operator actuatable switch is actuated, the cam which closes the holding current circuit switch being so shaped that said switch is held closed for a time interval substantially equal to theduration of the thread trimming operation and then causes said switch to open to deenergize said motor and terminate the thread trimming operation, and meansin series with said operator actuatable switch for rendering'the latter inoperative to start said motor when the sewing machine drive mechanism is operating.

27. The thread trimming device according to claim 15 wherein said control means further includes an electricallyy energizable motor effective when energized to rotate the* aforesaid'plurality of rotatable' cam elements, said cam* elements being coupled to the motor shaft for rotation therewith, an operator actuatable switch effective when lactuated to start said motor by connecting the motor energizing Winding to a source of electrical energization, and a switch closable by one of said plurality of rotatable cams for establishing a holding current Acircuit between said motor winding and source of'electrical energization in the time interval duringwhich said operator lactuatable switch Vis actuated, the cam which closes the holding current circuit switch being so shaped that Said switch is heldclosed for a time interval substantially equal to the duration of the thread trimming operation and then causes said switch to open to deenergize said motor and terminate the thread trimming operation, a switch ganged to said holding current circuit switch and operable therewith for rendering the sewing machine inoperable during the thread trimming operation by actuating a device which locks the sewing machine treadle to thereby prevent operation of the same by the sewing machine operator.

References Cited bythe Examiner UNITED STATES PATENTS 2,3 46,594 4/ 44 McCann 112-252 1 8 4/46 Stahl et al. 112-252 X 5 5 5 Artzt 112-252 9/ 5 8 Ketterer 112-252 8/ 62 Bi11i 66--145 X FOREIGN PATENTS 1/ 19 Germany. 2/ 19 Germany.

10 JORDAN FRANKLIN, Primary Examiner.

DAVID I. WILLIAMOWSKY, Examiner.

Claims

1. IN COMBINATION WITH A SEWING MACHINE, A THREAD TRIMMING DEVICE FOR SEVERING THE NEEDLE THREAD OF THE SEWING MACHINE COMPRISING, AN ELECTRICALLY ENERGIZABLE HEAT GENERATING ELEMENT, SHIFTABLE SEWING MACHINE PRESSER FOOT MEANS FOR SUPPORTING SAID ELEMENT IN OPERATIVE POSITION IN CLOSELY SPACED RELATIONSHIP TO THE UPPER SURFACE OF AN ARTICLE BEING STITCHED, ENERGIZING MEANS EFFECTIVE WHEN ACTUATED TO COUPLE SAID ELEMENT TO A SOURCE OF ELECTRICAL ENERGIZATION, CONTROL MEANS COUPLED TO SAID ENERGIZING MEANS AND UNDER THE CONTROL OF THE SEWING MACHINE OPERATOR FOR SELECTIVELY ACTUATING SAID ENERGIZING MEANS, AND MEANS FOR SHIFTING THE NEEDLE THREAD AGAINST SAID HEAT GENERATING ELEMENT WHEN SAID SHIFTABLE PRESSER FOOT IS IN A FIRST SELECTED POSITION, WHEREBY, WHEN SAID SHIFTABLE PRESSER FOOT IS IN SAID FIRST SELECTED POSITION, WHEN THE NEEDLE THREAD IS IN ENGAGEMENT WITH SAID HEAT GENERATING ELEMENT, AND WHEN SAID CONTROL MEANS IS ACTUATED, SAID ELEMENT IS ENERGIZED AND RENDERED EFFECTIVE TO BURN THROUGH THE NEEDLE THREAD.