US2438833A - Thread pull-off mechanism for sewing machines - Google Patents

Description

March 30, 1948 R, WOOD 2,43s,s33

THREAD PULL-OFF MECHANISMS FOR SEWING MACHINES Filed Aug. 21, 1945 2 Sheets-Sheet l March 30, 1948. A. R. WOOD THREAD PULL-OFF" MECHANISMS FOR SEWING" MACHINES 2 Sheets-Sheet 2 Filed Aug. 21, 1945 BUTTON/IDLE SL/T Patented Mar. 30, 1948 THREAD PULL-OFF MECHANISM FOR SEWING MACHINES Alfred R. Wood, Bridgeport, Conn, assignor to The Singer Manufacturing Company, Elizabeth, N. J a corporation of New Jersey Application August 21, 1945, Serial No.-61 1,;7 2 4 1 Claims.

This invention relates to buttonhole sewing machines, more particularly cf the automatic lock-stitch straight type, which is adapted to produce high quality buttonholes used most cqllmmonly in mens shirts, collars, cuffs and the li e.

"The type of stitch used to form this high quality buttonhole is generally referred to in the trade as the pyramid-purl lock-stitch. In this type of stitch-i'for-mation, the needle-thread take-up is required not only to draw up the needle-thread loops after they have been interlocked with the bobbin-thread, but also to draw such loops entirely through the work, pulling loops of bobbin-thread through to the upper side of the Work, so that in the finished seamthe needlethread will lie in substantially a straight line intermediate the rows of zigzag needle-punctures, while loopsof bobbin-thread emergefrom the needle-punctures at the upper side of the work and embrace the straight needle-thread. To .efiect this stitch-formation, it is necessary that the tension imposed upon the bobbin-thread be light, while the tension imposed upon the needle-thread be very strong. To further assist in properly concatenating the needleand bob bin-threads, it has been common to employ a bobbin-thread pull-off mechanism, which is designed to operate once during each stitch-forming cycle to pull from the bobbin a. length of thread to be absorbed into the stitch when the needle-thread loop is pulled up by the usual take-up. The presence of this slack bobbinthread available after the pull-off member is retracted permits a reduction in the amount of tension required on the needle-thread. This is advantageous inasmuch as it minimizes thread b ea a Thesuccessful operation of the bobbin-thread pull-01f is materially affected by the inherent elasticity ef the thread being used. The effect of using a bobbin-thread having considerable elasticity, or one in whichthe elasticity varies somewhat throughout its length, is that unequal lengths of thread are pulled from the bobbin u ing the fo mation o he tche n t utto-nhele. The result of a variation in the length of thread pulled off is that, in the finished buttonhole, the needle-th ead lies in a line which is wavy relative to the buttonhole slit. This defect is immediately discernible to the naked eye and t r fe e ma er al yreduc s t e q y of the finished bu tonh l herefqre, it s th pri ary b ect of th present inv ntion to pro id a imp otedmlleqfl mechanism which is effective to draw a uniform length of bobbin-thread .from the supply during each stitch-forming cycle, whereby a finished buttonhole is produced having the p ramid-pu l formed in a straight line substantially parallel to and uniformly spaced from the buttonhole slit.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set .forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.v

In e a m a n draw n s:

Fig. 1 represents a front .elevational view, partly in section, of a buttonhole, machine equipped wit my i prove bob i -thread P 1 oif mechanism. e

Fig. 2 represents a bottom plan yiew, partly in section,showing theconnections for actuating the pull-off blade.

Fig. 3 represents avertical sectional view taken substantially along the line (3+3, 1, illustrating the mechanical opener mechanism for the loop-taker and also the 1 68. 5 employed for rendering the thread pull-01f Lblade inefiective.

Fig. 4 represents a fragmentary view of a buttonhole, showing the manner .in which the needle-thread and bobbin thread are cpncatenated to form a pyramid-purl.

Fig. 5 represents a. vertical sectional view taken substantially along the line 5-75, Fig. 3.

Fig. 6 represents anenlarged top plan .view of the loop-taker thread-case and carrier therefor,

showing the desired shape oi the otht iqllstraining member and the :leaf-springpby which the bobbin-thread is maintained in position in said rotation-restraining member.

Fig. '7 represents an enlarged leitside elevational view, partly in section, of the c-shaped thread-guiding projection on, the thread-case between the spaced limbs oi which operates the bobbin-thread pul1=qff blade.

Fig. 8 represents a sectional view taken substantially along the line .898, Fig. 3,

Fig. 9 represents a right side elevational View, partly in section, of the ,stitcheiorming instrumentalities, showing the bobbin-thread pull-off blade in its maximumthread pull-off position.

Fi 10 is a view similar to 9,.but with the Dull-o1? blade shifted laterally to its ineffective p ition. in which position the blade is out of the range of the lead of the bobbin-thread between the spaced limbs of the C-shaped threadguiding projection on the thread-case.

Referring to the drawings, the machine chosen for the purposes of the present disclosure is constructed substantially in accordance with that forming the subject of my United States Patent No. 241L493, issued November 19, 1946, and has a frame including a bed ll provided with a supporting lug l2. J ournaled in a bushing 13 pressed into the supporting lug I2 is a rotary loop-taker shaft l4 geared to be operated by an arm-shaft (not shown) at a speed twice that of the armshaft. As clearly shown in my above mentioned patent, the arm-shaft is connected at the headend of the machine to endwise reciprocate a thread-carrying needle 45 which is adapted to be vibrated in a direction crosswise of the bed ll. Cooperating with the needle [5 in the formation of lock-stitches is a loop-taker, indicated generally as l5, of the rotary lock-stitch type, which loop-taker is fast on the rotary shaft M.

The work to be buttonholed is adapted to be held in a work-clamp comprising the usual lower work-plate l1 and the upper clamp-foot 18, Fig. 1. The work-clamp is slowly moved in step-bystep fashion under the endwise reciprocatory and laterally vibratory needle 15, and relative to the usual needle-aperture l9 in the throat-plate 20, first away from the machine-standard and then towards the machine-standard to cause the first and second rows of side zigzag stitches to be laid side by side in the work. The work-clamp derives its sten-by-step movements from the usual feedcam 2| through a link 22, Fig. 2, connected at one end to a slide-block 23 associated with the lower work-plate I! and operable in a slideway 24 provided in the bed H.

As previously-mentioned. the stitch-forming mechanism of the machine illustrated comprises the endwise reciprocatory and laterally vibratory thread-carrying needle I5 and the complemental rotary hook I6. The rotary hook is adapted to seize the thread-loop presented by the needle and expand such loo for passage about the under thread-mass contained in the stationary thread-mass enclosing means of the rotary hook. The thread-mass enclo ing means shown in the drawings forms the subject of my United States Pa ent No. 2.419.698 dated April 29, 1947, and

therefore only sufficient reference will be made in this case to this means as will be reouired to give an understanding ofthe operation of the bobbin-thread pull-ofi'. Suffice it to say that the thread-mass enclosing means comprises a cupshaped carrier-member 25 and a telescopically disposed thread-case 25, defining between them a thread-mass cavity into which is inserted the usual bobbin or cop. To restrain the threadmass enclosing means against rotation with the rotary loop-seizing beak of the loop-taker, the carrier-member 25 has extending upwardly from itsperiphery a substantially C-shaped projection 21, the upper portion of which is adapted to extend between the free ends of a pair of stop-plates 28 and 29 (Fig. 1), adjustably secured to the bed II of the machine-frames The C-shaped projection 2'! is vertically channeled to receive a, correspondingly shaped upstanding projection 39 formed on the thread-case 25.

As fully disclosed in my above mentioned U. S. Patent No 2,419,698 and shown in Figs. 9 and 100i this case, the bobbin-thread emerging from the usual thread-aperture in the thread-case 26 is directed beneath a tension-spring 3!, then behind a thread-guiding pin 32, upwardly through a threading-slit 33 provided in the thread-case projection 30, and thence beneath the free end of a leaf-spring 34 fastened to the upper limb 35 of the projection 30. As will be seen in Figs. 9 and 10, the thread-guiding pin 32 and the leafspring 34 function to maintain the bobbin-thread adjacent theinner end of the threading-slit 33, which position of the thread is advantageous as regards the successful operation of the bobbinthread pull-oil now to be described. Also, the leaf-spring 34 serves to lightly nip the bobbinthread and thus prevent the accidental unthreading of the upper limb 35.

Disposed to operate between the spaced bobbin-thread-directing guides defined by the upper and lower limbs 35 and 35 of the C-shaped projection 3B is a curved thread pull-off blade 31 having a thread-cam edge 38 formed adjacent its free end. At its other end, the pull-off blade 3'! merges into an offset shank 39 (Fig. 3) provided with an elongatedhole 4e and an inturned positioning lip 4|; the lip being adapted to enter a slot 42 formed in the outer end of a carrierlever 43 which embraces and is freely journaled at its inner end on. the exposed end of the hookshaft bushing I3. A clamp screw 44 passing through the elongated hole 40 and threaded into i "ing position between the limbs 35 and 36 of the G-shaped projection 30. When the pull-on blade 31 is advanced from its retracted position, shown in full lines in Fig. 5, to its advanced position, shown in dotted lines in the same figure, the thread-cam edge 38 is adapted to contact and deflect laterally the portion of the bobbin-thread leading from the lower to the upper limb of the C-shaped projection 39 and form a bight in the thread between the limbs of the projection, in the manner shown in Fig. 9. The blade 31, in forming the bight in the bobbin-thread, draws from the supply within the thread-case 26 a length of thread sufficient to form a bobbin-thread loop of a size such that it may be pulled through to the upper side of the work (Fig. 4), so that in the finished seam the needle-thread will lie in substantially a straight line adjacent the buttonhole slit. It will be noted that the limbs 35 and 33 of the C-shaped projection 39 are rather closely spaced apart. This is advantageous for the reason that the bobbin-thread extending between the limbs 35 and 36, as shown in dotted lines in Fig. 9, is relatively short. It is, in fact, so short that, when the thread-cam edge 38 of the pull-off blade engages the thread, any inherent elasticity in the thread does not militate against the drawing of a uniform length of thread from the supply during each stroke of the pull-off blade.

The mechanism for actuating the bobbinthread pull-oil blade 31 preferably comprises a counterbalanced crank 45 (Fig. 5) having a crank-pin 46 connected by a link 41 to a pin 48 threaded into the carrier-lever 43. The counterbalanced crank 45 is carried on the outer end of a horizontally disposed rotary actuating shaft 49 journaled in a bearing bushing 59 pressed into the supporting lug l2. Secured on the other end of the actuating shaft 49 is a gear 5| in mesh with a half-size gear =52 fast on the -hook--shaft 14. Through the mechanism just described, rotation -of the hook-shaft l4 imparts to the actuating shaft 49, through the gearing -51 and 52, "rotary rotated, the counterbalanced crank 45 imparts to thecarrier-lever 43, through the link 4'Iand pin 43,a motion causing the carrier-lever to oscillate about thebushing 1-3. The pull-off blade 31,

which is secured to the carrier-lever, is thereby swung about an axis coaxially with the rotary hook l6 and is 'timedto begin its advance as the needle is starting down and to completeits advance at about the time the needle reaches'the limit of its downstroke. The pull-off blade 31 dwells in its advanced position '(dotted lines in Fig. while the needle is throwing out a loop of upper thread for seizure by the rotary hook Hi. The pull-off then retracts so that slackbobbinthread is available to be absorbed into the next stitch when the needle-loop ispulled upby the usual needle-thread take-up mechanism. At the time of initial engagement of the-pull-ofi' blade 37 with the bobbin-thread, said blade is moving at a speed considerably less than that of the rotary hook l6. This fact coupled with thegrad ual incline of the thread-cam edge 38, results in the pull-off blade engaging the bobbin-thread with a. smooth action, thusavoiding a jerking of the bobbin-thread and minimizing any tendency toward overrunning or spilling of thread'bythe bobbin or cop.

Provision is made for rendering the pull-off blade "31 ineffective during the sewing ofthebarring stitches at each'end of the buttonho-le ;so that the locking points of these stitches will not be pulled through the work as are the sidestitches of the buttonhole. To this end,-theworkingposition of the carrier-lever 43 is shifted longi tudinallyof the bushing l3 so that the free end of the pull-off .blade will,'in its advance miss the bobbin-thread, as shown in Fig. 10. To efiect this shifting of the pull-ofi blade 31, the hub of the carrier-lever .43 is formed with a circumferential groove 53 which is "entered by the half round recessed portion of an arm -54 '(Fig. 18) on a slide-shaft 55 journaled in thesupporting lug 1 on a stud 59 threaded into the .bed [I The lever 58, at itsfree end, is longitudinally recessed, as at 60, to adjustably receivea cam-,followerlil having an elongated aperture 62 through which passes a clamping screw 63 threaded into thelever 5B. The camefolloweris disposedtobe engaged by a cam-section 64 secured by screws'54' on'the feed-cam "2|. While only .One cam-section is shown, it will be understood that 'twocam-sec- .tions are employed, one for each barring operation. 'In the operation of the machine, the "feedcam is ,rotated in the direction of the arrow in Fig.2, once during each complete buttonholing cycle. Whenthe cam-section B4 on thefeed-cam 2i engages the cam-follower 6|, the swing-lever 58 ismoved in a direction away-from the feed-- cam, causing the roller 51 to move into engagement with the head .56 of the slide-shaft 5,5 shift the same outwardly against the action of a coil-spring 65 acting between a collartfi on-the slide-shaft and the supporting lug 12. When -rier 25 on thecast-on side thereof.

the slide-sha'ft ts 'isishlfted, the. carrier-lever :43,

ithrough the mediumibftheiarm 754, is moved out- =-wardly on the bearing bushing l3 and to the -=extent that the point ofthe pull-off bladei3'l entirely miss'es :the bobbin-rthread (Fig. 10) and no bobbin-thread is pulled off during the formation of the barring stitches. After the completion of thelast barring :s'tit'c'h and the camsectionifi l has moved beyond the cam-:follower 61, the coilspring acts to return the pull-off blade 31 to its efiectivepo'siti'on, which position is determined 'by the'hub of the arm 5 striking the supporting lug :12. Asshown'inFig. 3, the pin-48 slides relative to the upper end-'of-the link 41 during the shifting of the pull-off blade and, consequently, the driving -relationship of the pull-off bladeactuatin'g mechanismds-not interrupted. It will be understood that the timing of the shaft of the pull-01f blade fromeffective to ineffective position adapted --to be housed in "a thread-mass enclosing means including; athread-case "26 and a carrier 25 therefor; the thread-case and carrier being restrainedagainst-rotation with the rotary loopta-ker 18 by means of the loosely interengaging projection 2-1 and stop-plates *28 and 29. The

thread-case audits carrier have-a normal tendency to rotate with --the loop-taker, thereby causing therotation-restraining projection 21 tobear In order to obtain a free passage 'on each side of the projection 21 for the --unolostructed "free travel of the needle-thread loop-aboutthe thread-case and its carrier during stitch-formation, the thread-case and its carrier are=intermittently oscillated, for a limited extent, in a--di-re'ction opposite'to the direction "of rotation of the loop-taker. This oscillation is effected by means of a mechanical opener which forms the subject ofmy divisional application Serial No. 678,618, filed June 22, 1946, and-comprises an opener-arm 6'! (Figs. 1 and 3) which is adjustablyclamped at its lower end in a :split socket-member 68 fast on the outer end of a rock-shaft -Bil journaled in a horizontal bushing 10 presseddn tothe supporting lug l2. At its upper end, theopener-arm 6'! isbent, as at ll,

to provideahook-shaped end extending toward the thread-case '26; the hook-shaped end being -notched,-as at l-2, "Fig. 1, toform spaced resilient fingers 13 "adapted to enter an opener-arm receiving pocket 14 formed in the thread-case car- The fingers "are preferably shaped'so'that there is asmooth cam-like "initial :engagement of the upper fin- .ger with eneside o'f the threadcase carrier pocket 14 to i-nitiate'auoscillation of the thread-case carriei in a'direction reverse to the direction of rotation of the hook-body, and that following tained ---stationary substantially midway between the stop-plates2i3 and 2-8. The spaced resilient fingers l3 serve to provide a relatively noiseless mechanical-openenas well as one which maintains the rotation-restraining projection onlthe "thread-mass enclosing means stationary and in position such that an open thread passage exists on'both sides-of the projection for the ireeunobstructed travel of the needle-thread loop.

. understood that I have invented a bobbin-thread pull-off mechanism which is accurate in its operation, drawing from the supply an equal length of thread during each stitch-forming cycle, regardless of the degree of elasticity inherent in the thread. The upstanding C-shaped rotationrestraining projection on the thread-case carrier provides closely spaced thread-confining limbs between which operates the thread pull-off blade. In addition, the rotation-restraining projection provides a surface which functions to retard one limb of the needle-thread loop as it is being cast off the thread-case, and this retardation minimizes twisting of the thread comprising the loop, thereby preventing the formation of loops or knots in the pyramid-purl of the buttonhole. Furthermore, since the upper limb 35 of the rotation-restraining projection is positioned adjacent the bottom of the throat-plate 2!], the short cut end of the bobbin-thread, which is produced by the actuation of the usual threadcutting devices following the completing of the buttonhole, is retained by the slight nipping action of the leaf-spring 34 near the work and not permitted to drop down out of control. This control of the bobbin-thread insures the proper operation of the pull-off mechanism on the first stitch of the next buttonholing cycle.

Having thus set forth the nature of the invention what I claim herein is:

1. A sewing machine having, in combination, a thread-carrying reciprocatory needle, a circularly moving loop-taker cooperating therewith, a bobbin-thread-mass enclosing means journaled in said loop-taker, a rotation-restrainingprojection on said thread-mass enclosing means having a pair of spaced thread-directing guides, and a thread pull-off member adapted to engage the bobbin-thread between said thread-directing guides during each stitch-forming cycle.

2. A sewing machine having, in combination, a thread-carrying reciprocatory needle, a circularly moving loop-taker cooperating therewith in the formation of lock-stitches, a bobbinthread-massenclosing means journaled in said loop-taker and restrained against rotation therewith, a projection extending from said bobbinthread-mass enclosing means and providing a pair of spaced thread-directing guides, and a thread pull-off member arranged to engage the bobbin-thread between said thread-directing guides once during each stitch-forming cycle.

3. A two-thread sewing machine having, in combination, a thread-carrying reciprocatory needle, a rotary loop-taker having a loopeseizing beak cooperating with said needle in the formation of lock-stitches, a bobbin-thread-mass enclosing means journaled in said loop-taker and restrained against circular movement therewith, a pair of bobbin-thread-directing guides disposed outside the field of action of the loop-seizing beak of said rotary loop-taker, and a thread pull-01f member arranged to engage the bobbinthread between said thread-directing guides to draw thread from the bobbin once during each stitch-forming cycle. I

4. A two-thread sewing machine having, in combination, a thread-carrying reciprocatory needle, a circularly moving loop-taker having a loop-seizing beak cooperating with said needle in the formation of lock-stitches, a bobbin;

thread-mass enclosing means journaled in said loop-taker and restrained against rotation there- With, said bobbin-thread-mass enclosing means including a thread-case having a cylindrical side wall, a projection extending from said threadcase and providing a pair of spaced limbs disposed beyond the confines of said cylindrical side wall, a thread-directing guide in each of said limbs, and a thread pull-ofi member adapted to engage the bobbin-thread between said threaddirecting guides once during each stitch-forming cycle.

5. A sewing machine having, i combination, a thread-carrying reciprocatory needle, a circularly moving loop-taker cooperating therewith in the formation of lock-stitches, a bobbinthread-mass enclosing means journaled in said loop-taker, a rotation-restraining projection on said bobbin-thread-mass enclosing means terminating in substantially C-shape at it free end, thereby defining a pair of spaced limbs each having a thread-directing guide, and a thread pulloff member adapted to engage the bobbin-thread between said thread-directing guides to draw thread from the bobbin once during each stitchforming cycle.

6. A sewing machine having, in combination, a bed fitted with a throat-plate, a thread-carrying reciprocatory needle, a circularly moving loop-taker cooperating with said needle in the formation of lock-stitches, a bobbin-thread-mass enclosing means journaled in said loop-taker and restrained against circular movement therewith, a first bobbin-thread directing guide disposed adjacent saidthroat-plate, means for preventing the accidental unthreading of said first threaddirecting guide, a second bobbin-thread-directing guide spaced from said first bobbin-threaddirecting guide, and a thread pull-oil" member arranged to engage the bobbin-thread between said first and second bobbin-thread-directing guides to draw thread from the bobbin once during each stitch-forming cycle.

7. A sewing machine having, in combination, a bed fitted with a throat-plate, a thread-carrying reciprocator needle, a circularly moving loop-taker cooperating with said needle in the formation of lock-stitches, a bobbin-thread-mass enclosing means journaled in said loop-taker and restrained against circular movement therewith, a first bobbin-thread directing guide disposed adjacent said throat-plate, a leaf-spring cooperating with said first thread-directing guide for preventing accidental unthreading of said guide, a second bobbin-thread-directing guide spaced from said first bobbin-thread-directing guide, and a thread pull-oif member arranged to engage the bobbin-thread between said first and second bobbin-thread-directing guides to draw thread from the bobbin once during each stitch-forming cycle.

8. A sewing machine having, in combination, a bed having a throat-plate, means providing a rotation-restraining notch positioned adjacent said throat-plate, a thread-carrying reciprocatory needle, a circularly moving loop-taker having a loop-seizing beak cooperating with said needle in the formation of lock-stitches, a bobbinthread-mass enclosing means journaled in said loop-taker, a rotation-restraining projection on said bobbin-thread-mass enclosing means and disposed to enter the notch adjacent said throatplate, a first thread-directing guide provided on said rotation-restraining projection adjacent said throat-plate, a second thread-directing guide on said projection spaced from said first thread- -directing guide, and a thread pull-oil member adapted to engage the thread intermediate the firstand second thread-directing guides.

9. A sewing machine having, in combination, a thread-carrying reciprocatory needle, a circularly moving loop-taker cooperating therewith in the formation of lock-stitches, a bobbin-threadmass enclosing means journaled in said looptaker, a rotation-restraining projection on said bobbin-thread-mass enclosing means and having spaced limbs, an open-sided threading-slit cut into said spaced limbs 50 that the closed end of the threading-slit is adjacent the ends of the limbs, means for maintaining the bobbin-thread adjacent the closed end of said threading-slit, thereby to provide spaced bobbin-thread-directing guides, and a thread pull-off member adapted to engage the bobbin-thread between the limbs of said rotation-restraining projection.

10. A sewing machine having, in combination, a thread-carrying reciprocatory needle, a rotary loop-taker cooperating therewith in the forma- 10 tion of lock-stitches, a bobbin-thread-mass enclosing means journaled in said loop-taker, a rotation-restraining projection on said bobbin-v thread-mass enclosing means terminating in substantially C-shape at its free end to provide spaced limbs, an open-sided threading-slit formed longitudinally of said limbs and ending short of the ends of said limbs, means associated with each of the limbs for maintaining the thread in the closed end of said threading-slit, and a thread pull-off member adapted for engaging the thread between the limbs of the rotationrestraining projection.

ALFRED R. WOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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