US3628480A

US3628480A - Loose stitch forming mechanism for lockstitch sewing machines

Info

Publication number: US3628480A
Application number: US53604A
Authority: US
Inventors: William C Van Ness
Original assignee: Singer Co
Current assignee: SSMC Inc
Priority date: 1970-07-09
Filing date: 1970-07-09
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: GB1354534A

Abstract

A lockstitch sewing machine with needle and bobbin thread metering and controlling mechanisms whereby selected looseness may be provided in the threads of the resulting stitched seams including the presence of precisely controlled amounts of surplus slack thread in the seam.

Description

United States Patent [56] References Cited UNITED STATES PATENTS 4/1916 Rh0des.........................

William C. Van Ness Parsippany, NJ. 53,604

Inventor [21 Appl. No.

[22] Filed July 9, 1970 [45] Patented Dec. 21,197]

[73] Assignee The Singer Company New York, N.Y.

Robert E. Smith [54] LOOSE STITCH FORMING MECHANISM FOR LOCKSTITCH SEWING MACHINES ABSTRACT: A lockstitch sewing machine with needle and 11 Claims, 10 Drawing Figs. bobbin thread metering and controlling mechanisms whereby selected looseness may be provided in the threads of the resulting stitched seams including the presence of precisely controlled amounts of surplus slack thread in the seam.

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SHEET 1 OF 3 INVENTOR WIIIICIm C. Van Ness Fig.

a ATT RNEY WITNESS: Mm, Wan/M7"? PATENTEU m2] I97! SHEET 2 0F 3 INVE N TOR Willjqm C. Van Ness AT ORNEY PATENTED UEEZI IHTI SHEET 3 BF 3 INVENTOR wllllom C. Van Ness LOOSE STITCH FORMING MECHANISM FOR LOCKSTITCI-I SEWING MACHINES BACKGROUND OF THE DISCLOSURE In a conventional lockstitch sewing machine in which the needle thread is directed in sequence to a thread-tensioning device, a thread takeup device, and thence to the needle, adjustment of the thread-tensioning device can influence how tightly the stitches are set into the fabric being sewn. With such known arrangements, however, looseness with slack or surplus thread cannot be provided in the seam by regulation of the thread-tensioning device because when this slack thread condition is approached, a condition of uncontrolled loop formation of the sewing threads can occur with an unsightly seam being produced, and usually thread breakage within a relatively few stitches.

The advent of recent advances in the art of fabric treatments, such as permanent press finishes and the like, has introduced into the art of sewing the need for means for providing stitching which includes controlled surplus or slack thread immediately after the stitching operation so that after subsequent application of pressure, heat, chemicals and chemical changes, the seams will not become puckered, but will lie perfectly flat when the treatment is finished.

The previously known use of stitch-supporting fingers for the purpose of providing loose lockstitches has proven cumbersome, costly and unsuccessful in providing the accuracy of control required particularly over the entire range of loose ness that may be required of a modern high-speed lockstitch machine.

BRIEF SUMMARY OF THIS INVENTION The present invention provides for the formation of controlled surplus in the sewing threads of a lockstitch seam by the use of control devices effective on the sewing threads to meter the desired surplus thread into the seam while continuously maintaining control of the threads to prevent looping.

Metering of the needle thread is obtained with this invention by an arrangement which directs two successive lengths of the needle thread to the action of the takeup means with a thread nipping device interposed between the two lengths of thread and effective to prevent retrograde motion of the thread, i.e., to pass thread only in a direction toward the needle. With this arrangement, surplus thread in regulated amounts may be drawn from a supply into the thread-manipulating system of the sewing machine in a manner which is not related to the setting of the stitches and in a manner such that the forces necessary to draw in the thread do not work to tighten the stitches being formed. Nonetheless, the system of this invention applies sufficient tension and control on the sewing threads during the entire stitch-forming cycle that uncontrolled flow of the thread and consequent looping is obviated.

This invention also provides for metering of the bobbin thread in a lockstitch-forming machine early in or at the initiation of each successive cycle of stitch formation which has been found to assist markedly in the formation of relaxed loose limbs of each of the needle and bobbin threads of a lockstitch seam.

Specifically, this invention provides for a device in the form of a unitary attachment which may be applied conveniently to any conventional lockstitch machine to provide operation thereofin accordance with this invention.

Because only minor adjustments are required to the existing thread-handling mechanism of a lockstitch machine in order to accommodate the present invention, a machine with the present invention applied thereto may also be threaded in such a way as to bypass the thread-metering facilities of this invention but yet retain the feature that the thread is directed twice to the action of the takeup member, and this to a manually selectable degree so that conventional tightly set stitching may be performed over an unusually wide range of machine-operating conditions.

With the above and additional objects and advantages in view as will hereinafter appear, this invention comprises the devices, combinations, and arrangements of parts hereinafter described and illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 represents an end elevational view of a lockstitch sewing machine having this invention applied thereto with the faceplate removed and portions of the frame illustrated in cross section,

FIG. 2 is a side elevational view of the sewing head portion of the sewing machine of FIG. 1,

FIGS. 3, 4, 5, and 6 are perspective views of fragments of the needle thread controlling instrumentalities of the sewing machine of FIGS. 1 and 2 with the parts shown in successively different positions during a typical cycle of stitch formation,

FIG. 7 is a side elevational view of a sewing head portion of a sewing machine having a modified form of this invention applied thereto with the needle thread shown as directed for the production of loose stitches,

FIG. 8 is a side elevational view of the sewing machine of FIG. 7 but with the needle thread shown as directed for the production of tight stitches,

FIG. 9 is a perspective view of the loop taker of the sewing machine of FIG. 1 showing the bobbin and needle threads at an early stage during stitch formation and including the bobbin thread pulloff element in its effective position for drawing off bobbin thread, and

FIG. 10 is a perspective view taken from the underside of the sewing machine work feed dog illustrating the manner in which the bobbin thread pulloff element may be carried thereby.

FIGS. 1 and 2 illustrate this invention as applied to a sewing machine in one preferred form of construction. These figures illustrate only the head end of the sewing machine and do not disclose, for instance, the driving connections between the in terrelated sewing mechanisms. Such driving connections between the needle, loop taker and work-feeding mechanism may be of any conventional arrangement and preferably may be as disclosed in the U.S. Pat. No. 2,394,51 l of Clayton, Feb. 5, 1946 to which reference may be had. This referenced U.S. Pat. No. 2,394,51 I also discloses a conventional needle thread manipulating arrangement which is supplanted by the novel mechanism of this invention.

Referring to FIGS. 1 and 2, 11 indicates the bed of a sewing machine from which raise a standard 12 supporting a bracket arm 13 which overhangs the bed and terminates in a hollow sewing head 14. A faceplate 15 is fastened in a position covering the hollow sewing head 14 as shown in FIG. 2.

Journaled in the bracket arm 13 is a main drive shaft 20 which carries fast thereon in the sewing head a counterbalance 21 with which is associated two crank pins; a crank pin 22 for reciprocating a needle, and a crank pin 23 for driving a takeup mechanism.

The needle reciprocatory crank pin 22 is embraced by a drive link 24 which is pivoted on a stud 25 extending laterally from a needle bar 26. The needle bar is endwise reciprocable in

bearing sleeves

27 and 28 in the sewing head and carries at the lower extremity an eye pointed thread carrying sewing machine needle 29.

The takeup driving crank pin 23 is embraced by one extremity of a takeup lever 30 which projects out of the hollow sewing head through a slot in the front wall and terminates exteriorly of the sewing head in a threadengaging eyelet 32. Pivoted as at 33 between the extremities of the takeup lever 30 is an anchor link 34 which is constrained on a pivot pin 35 fixed in the sewing machine bracket arm 13.

Also arranged in the sewing machine head is a presser bar 40 endwise movable in a bearing sleeve 41 and carrying a work engaging presser foot 42. A pressure regulating rod 43 of which an upper segment 44 is threaded into the sewing head projects into a bore 45 in the presser bar and serves to constrain a spring 46 therein for biasing the presser foot downwardly. A split block 47 secured by a clamp screw 48 to the presser bar serves three functions in the illustrated sewing machine in that first it engages the sewing head 14 to prevent turning of the presser foot; second it carries a threadengaging wire guide 49 which is secured by a screw 50 to the block 47 and which extends outwardly through a slot 51 in the sewing head to exert a regulation on the needle thread manipulation in accordance with the thickness of work fabric beneath the presser foot, and third, it overlies a bent wire link 52 which embraces a pin 53 extending from a presser-lifting lever 54 fulcrumed along the rear of the bracket arm 13 and adapted to be turned by a pull rod 55 which may be connected to any conventional treadle or knee shift device (not shown).

A flexible cable 56 is clamped by a screw 57 to the pin 53 on the presser-lifting lever 54. The flexible cable is directed through a guide tube 58 held on the sewing head by a bracket 59 and serves, as will be described in detail below, to release a tension device of this invention when the presser foot is raised.

As illustrated in FIG. 1, a loop taker is journaled in the bed 11 for cooperation with the needle 29 in the concatenation of threads into lockstitches. The loop taker may be of any conventional form and preferably is operated, as described in the above referenced U.S. Pat. No. 2,394,51 l to complete two revolutions during each reciprocation of the needle.

A throat plate 71 which is carried on the bed 11 to support work fabrics against the thrust of the needle is formed with a needle aperture 72 as shown in phantom line c FIG. 9 and is also formed with slots 73 to accommodate a work engaging feed dog 74. The feed dog is carried by a feed bar 75 which as shown in FIG. 1 is pivoted at 76 to a feed advance rock frame 77 which is secured on a feed advance rock shaft 78 journaled on the bed and serves to impart work feeding and return movements to the feed dog. At the other extremity, the feed bar 75 is pivoted to a link 79 which, in turn, is pivoted to a feed lift rock arm 80 secured to a feed lift rock shaft 81 journaled in the bed. The feed advance and feed lift rock shafts 78 and 81 may be actuated as described in the above referenced US. Pat. No. 2,394,5[1 to impart an oval path of motion to the feed dog 74 moving, as viewed in FIG. I to the right and upwardly Into engagement with a work fabric, remaining elevated while moving to the left to feed the work, then moving downwardly out of work engagement and returning to the right while lowered beneath the throat plate.

Referring to FIG. 2 and to the above referenced US. Pat. No. 2,394,51 I, the conventional needle thread handling mechanism of the sewing machine remains largely undisturbed by the present invention and therefore, the present invention may be applied readily to existing lockstitch sewing machines without requiring elaborate changes to the existing mechanisms.

Indicated at in FIG. 2 is a conventional needle thread tensioning device which is arranged in the usual location on the sewing head 14 and which includes a check spring 91 shiftable about a central stud 92 on which is arranged a pair of tread-engaging disks 93 and an adjusting nut 94 which ordinarily serves to regulate the pressure of a beehive spring on the stud for biasing the disk 93 against each other. When the present invention is applied to the sewing machine, the conventional thread-tensioning device 90 is used only for the effect of the check spring 91, and therefore, the beehive spring may be removed as shown in the drawings. The thread-engaging disks 93 may be retained as they provide an effective guide for the thread in conjunction with the check spring 91.

As shown in FIG. 2, from the check spring 91, the needle thread Nt is directed to the needle 29 in a conventional manner, first to the wire guide 49, then to one thread-engaging loop 95 of a double-thread guide 96 secured to the sewing head 14 beneath the takeup lever 30, then to the takeup lever eyelet 32, next to another thread-engaging loop 97 of the double-thread guide 96, through a wire guide 98 on the needle bar bushing 28 and to the needle.

The needle thread controlling mechanism of this invention, which is applied to a sewing machine in addition to the conventional thread-controlling means described above, is carried on a support plate 100. As shown in FIGS. 1 and 2, a guard 101 for the takeup lever 30 is secured to the sewing head 14 by fastening screws 102. The guard 101 has an arched rib 103 located outwardly on the path of the takeup lever and a flat base 104. The support plate may be fastened to the sewing head by the same screws 102 which secure the guard 101 in place. Additionally, the guard 101 is preferably spaced slightly outwardly of the support plate 100 by spacing a washer 105 at the top and by the double-thread guide 96 at the bottom and the base 104 of the guard 101 is transversely slotted as at 107 so that thread may be directed into the space between the base 104 of the guard 101 and the support plate 100. The base 104 must, in addition, be formed with a vertical slot 108 overlying the takeup accommodating slot in the sewing head. Moreover, the support plate must also be formed with a vertical slot which is in alignment with the vertical slot 108 and through which the takeup lever 30 extends.

On the upper portion of the support plate 100 above and to the left of the takeup lever 30, as viewed in FIG. 2, an auxiliary thread-tensioning device 110 is carried. The tensioning device 110 is termed auxiliary because in this invention the device 110 replaces the conventional tension device 90 as the agency giving rise to tension control in the needle thread.

The tension device 110 may be of any type known per se and preferably comprises a transversely slotted and threaded stud 111 on which a pair of thread-engaging disks 112 are arranged. A beehive spring 113 is carried on the stud between a washer 114 against the disks 112 and an adjusting nut 115 for regulating the spring pressure applied to the disks 112. The flexible cable 56 is directed preferably to the washer 114 of the thread-tensioning device for removing the pressure of the spring 113 from the disks whenever the presser foot is lifted.

A tab struck out from the supporting plate 100 is apertured to serve as a thread guide leading thread from a supply source (not shown) to the tensioning device 100. A wire thread guide 121 secured by a screw 122 on the supporting plate 100 beneath the tensioning device directs the thread from the tensioning device.

Mounted behind the supporting plate 100 on the right-hand side of the takeup lever on a fulcrum screw 123 is a bell crank 124 having one arm 125 formed with a thread-guiding loop 126 which projects through a slot 127 in the supporting plate 100. The other arm 128 of the bell crank extends upwardly beyond the top of the support plate and provides a finger grip 129 for adjustment of the position of the bell crank. Cooperating indicia 130 on the finger grip and on the support plate 100 provide visual indication of the operator influenced setting of the bell crank. A friction washer 131 on the function screw 23 or any other known arrangement may be provided for deterring accidental movement of the bell crank 124.

Carried on the supporting plate 100 above the slot 127 is a device indicated generally at which acts as a one-way thread-clutching device permitting passage therethrough of the needle thread only in one direction; i.e., toward the needle. The device 140 comprises a bracket 141 secured by screws 142 to the supporting plate 100 and formed with an out and upturned ear 143 for supporting a fulcrum pin 144 for a lever 145 fonned with thread-guiding notches 146, one at each end. The bracket 141 beneath each extremity of the lever 145 is formed with a tab 147, which tabs may be notched to guide the thread to and from the lever 145 and which additionally provide stops limiting pivotal movement of the lever.

Above the lever on the right-hand side of the fulcrum pin a 144 as viewed in FIGS. 2 and 4 is an abutment dog 150. The

dog is vertically slotted as at 151 to accommodate a clamp screw 152 by which the dog may be secured in selected position on the bracket 141. Two

fingers

153 and 154 struck out from the supporting plate 100 embrace the abutment dog 150 so that together with the clamp screw 152 the abutment dog can be adjusted only in a vertical direction. A horizontal slot 155 in the abutment dog 150 accommodates an eccentric head portion 156 of an adjusting crank 157. As shown in FIG. 4, a concentric stud 158 on the adjusting crank is journaled in an aperture 159 in the supporting plate 100. When the clamp screw 152 is loosened, turning of the adjusting crank 157 will, therefore, result in fine adjustment of the vertical position of the abutment dog so that the sensitivity of the one-way threadclutching device may be regulated. A very light spring 160 is preferably arranged between a tab 147 and the lever 145 to bias the lever toward the abutment dog 150.

The specific manner of threading a sewing machine equipped with this invention and the mode of operation is best illustrated abutment dog FIGS. 3 to 6. The needle thread N: is passed from a source of supply (not shown) to the auxiliary tensioning device 110, to thewire guide 121 thence under the path of oscillation of the takeup arm 30 to the thread-guiding loop 126 of the adjustable bell crank 124. The thread then is directed across the lever 145 of the thread-clutching device 140 between the lever 145 and the abutment dog 150 thereof and then downwardly to the check spring 91. As previously described, the thread is then directed through the pair of thread-guiding

loops

95 and 97 of the guide 96 and between the thread-guiding loops to the takeup eyelet 32, and thence to the needle.

In the sequence shown in FIGS. 3, 4, 5 and 6, the takeup lever 30 is shown respectively on the downstroke, at the very bottom of the downstroke, in the identical position as in FIG. 3 but on the upstroke, and at the very top of the upstroke. In FIG. 3 the takeup arm is shown in a position on the verge of engaging the limb of needle thread between the

guides

121 and 126. For comparison of the influence of the parts on the thread, three points along the thread are marked on FIGS. 3 to 6; point A being on the thread leading to the auxiliary tensioning device 110; point B being initially along the thread leading to the thread-clutching device 140; and, point C being initially along the thread leading to the check spring 91.

As shown in FIG. 4, when the takeup lever 30 engages the thread between the guides I21 and 126, the pull on the thread will cause the thread-clutching device 140 to nip the thread preventing any retrograde movement of the thread, and consequently a measured amount of thread will be drawn through the auxiliary thread-tensioning device 110 as indicated by the changed position of the point A on the thread.

As the takeup lever 30 begins to rise, as shown in FIG. 5, its acceleration will be at a maximum so that the thread-clutching device will immediately be opened and that increment of the thread metered through the auxiliary-tensioning device 110 will be drawn through the thread-clutching device and toward the check spring 91 as shown in FIG. 5 by the changed positions of the points B and C along the thread.

By adjustment of the position of the bell crank 124 the amount of thread metered into the system may be regulated. This amount of thread metered into the system may be varied from that amount required to set a tight stitch resembling that which is produced by a conventional sewing machine, to an amount several times greater than required for a tight stitch so that a stitch with many times the minimum quantity of thread may be formed.

As the takeup lever 30 rises to the top of the upstroke in FIG. 6, the lockstitch will be set or drawn into the work, and the unchanged position of point A as compared with FIG. 5 illustrates that no additional thread will be drawn into the system from the source of thread supply. The needle thread moreover will with this invention never be drawn into the system in an uncontrolled manner such as might result in the formation of uncontrolled thread loops on the fabric being stitched. The amount of looseness of the stitching may be accurately adjusted so as to match precisely the shrinkages which will be induced into the threads and fabrics by sub sequent treatments so that a final flat and pucker-free seam can be attained in the finished garment.

FIGS. 9 and 10 illustrate a bobbin thread pulloff mechanism which when used with the needle thread controlling device of this invention provides for an advantageous uniformity in the distribution of thread looseness as between the needle and bobbin threads of a lockstitch seam. As shown in FIG. 10, the

feed dog 74 of the work-feeding mechanism is formed with a transverse slot in the underside which slot is preferably not perfectly perpendicular to the direction of work-feeding movement of the feed dog but slightly canted relatively to the perpendicular. A thread-engaging wire 190 is fastened in the slot 180 so as to be positioned rearwardly of the needle aperture 72 in the throat plate 71. FIG. 9 illustrates the loop taker 70 as the loop-seizing beak thereof has entered a needle thread loop N! and includes a representation of the bobbin thread-engaging wire at the forward position of the feed dog. The wire 190 will, as shown in FIG. 9, loosen the bobbin thread Bt as it issues from the loop taker and this looseness in the bobbin thread early in each stitch-forming cycle eliminates resistance to passage of the needle thread loop Nt along the bobbin thread Br and upwardly into the work being stitched.

FIGS. 7 and 8 illustrate a modified form of construction of this invention, and moreover, illustrate alternative threading arrangements which are possible with this modified form.

The sewing machine illustrated in FIGS. 7 and 8 may be identical in construction and arrangement of conventional features to that illustrated in FIGS. 1 and 2. The similarity to the construction of the machine of FIGS. 7 and 8 to that of FIGS. 1 and 2 also extends to the conventional needle thread handling means including the needle thread tensioning device 90, the check spring 91, the wire thread guide 49, the doublethread guide 96 for leading thread to and from the eyelet 32 of the takeup lever 30. Like components of the sewing machine in the modification of FIGS. 7 and 8 have, therefore, been indicated by the same reference characters as applied hereinabove to the construction of FIGS. 1 and 2.

The needle thread controlling mechanism of this invention in the form shown in FIGS. 7 and 8 is carried on a support plate 200 which is formed with a protrusion 201 snugly accommodating a boss (not shown) on the sewing machine so that the support plate may be securely fastened on the sewing machine by a single-fastening screw 202 threaded into the boss. The support plate 200 is preferably L" shaped and arranged to extend closely adjacent to the path of oscillation of the takeup lever 30. An auxiliary thread tension device 210 is carried by the support plate 200 on the left-hand side of the path of the takeup lever 30 as viewed in FIGS. 7 and 3. The auxiliary tension device 210 may be identical to the auxiliary tension device 110 shown in FIGS. 1 through 6. A wire thread guide 212 is secured to the support plate 200 and accommodates several turns of the thread from a source of supply (not shown) to the auxiliary tension device 210, so as to provide a slight pretension and to remove kinks from the thread.

Fulcrumed on a screw 223 on the support plate 200 is a bell crank lever 224 having one arm 225 formed with a threadguiding loop 226 arranged closely adjacent to the auxiliary thread tension device 210 and adjustable vertically relatively thereto upon turning of the bell crank lever 224. A second arm 228 of the bell crank protrudes beyond the support plate 201) and is formed with a finger grip 229. Indicia 230 on the finger grip and on the support plate serve to delineate the position in which the bell crank lever is set. A friction washer 231 on the screw 223 deters accidental movement of the bell crank.

Indicated at 240 in FIGS. 7 and S is a thread-clutching device which differs only in specific details of construction from the thread-clutching device 140 of FIGS. 1 through 6.

The thread-clutching device 240 includes a lever 245 notched at each extremity to accommodate the needle thread and fulcrumed on a pin 244 which is secured between the support plate 200 and an ear 243 struck out therefrom. A thread camming projection 248 is struck out from the support plate 200 adjacent the upper extremity of the lever 245 to facilitate insertion of a thread in the upper notched end of the lever 245. A light coil spring 260 bears against the lever 245 and biases the lever against an abutment dog 250 secured by a screw 252 to the support plate 200. A spring-adjusting bell crank 270 is fulcrumed on a screw 271 on the support plate for regulating the pressure exerted on the lever 245 by the coil spring 260.

In FIG. 7 which illustrates the threading of the device of this invention for the production of loose stitching, the principal differences of this modification from the form of construction shown in FIGS. 1 through 6 will be apparent. The needle thread Nt is directed from the auxiliary tensioning device 210 to the thread-guiding loop 226 of the bell crank 224, and thence, directly to the lever 245 of the thread-clutching device. This limb of the needle thread N! passes over the takeup lever 30 and intersects the path of motion thereof. Preferably, this limb of the thread additionally passes between the support plate 200 and a thread constraining finger 280 struck out from the side of the support plate 200.

The thread is then passed along the lever 245 and as in the previously described version, to the conventional thread-tensioning device 90 and, as described above, then to the takeup eyelet 32 and to the needle. As in the previous version, the conventional thread-tensioning device 90 is not used as a tension producing device so that its beehive spring may be removed.

The angles which the thread makes approaching and leaving the lever 245 differ markedly in the modification of FIG. 7 as compared with the version shown in FIGS. 1 through 6. Assuming that uniform tension exists in the thread, the sharper angle of the thread approaching the lever will result in a greater component of force being applied to the lever by the approaching thread than by the thread leaving the lever, and as a result, the thread-clutching device will prevent retrograde movement of the thread more readily under such conditions when arranged as shown in FIG. 7.

In FIG. 7 the takeup lever 30 is shown substantially at the top of stroke so that the limb of needle thread from the threadguiding loop 226 to the thread-clutching device 240 will be distended by engagement with the takeup lever 30, and the loop of needle thread passing through the takeup eyelet 32 will also be distended. With this modification, therefore, the surplus thread for formation of loose stitches will be metered into the thread-controlling system through the auxiliary tensioning device 210 during the same interval that the preceding stitch is being drawn up into the work. The thread-clutching device 240 will, however, separate these two functions. The thread drawn or metered through the auxiliary tension device 210 on one upstroke of the takeup lever, will be available in the thread-controlling system for the formation of a loose stitch on the next succeeding upstroke of the takeup. In fact, the check spring 91 which is fully distended in the stitchsetting position illustrated in FIG. 7, will return as soon as the takeup lever 30 begins to descend and in returning the check spring 91 will draw the freshly metered slack thread through the thread-clutching device 240. Since the freshly metered thread will be available to the takeup lever and to the needle early during the needle downstroke, loose thread will be available to facilitate needle penetration. The slack which is metered into the system during the stitch-setting portion of each cycle will remain available during the entire cycle so as toinfluence the formation of the succeeding stitch with surplus thread therein in the same manner as previously described with respect to the form of construction illustrated in FIGS. 1 to 6. The amount of slack thread metered into the system at each stitch can be regulated by changing the position of the bell crank 224 by shifting the finger grip 229 thereof.

FIG. 8 illustrates the identical mechanism of FIG. 7 but with the needle directed differently. The threading shown in FIG. 8 will result in needle thread handling generally in the conventional fashion, i.e., with the stitches being set with ordinary tightness into the work, but with the novel feature that the amount of thread in the needle thread handling system may be changed at will so that this construction may be applied to sewing machines having a wide range of different work thickness capacities, widely different needle bar strokes, etc.

In FIG. 8, from the thread-guiding loop 226, the needle thread is directed over the takeup lever 30 over the threadguiding finger 280 and then directly to the conventional thread-tensioning device 90, which as in previously described embodiments, has its thread-tensioning spring removed or rendered ineffective. The thread is then directed, as described above, to the action of the check spring 91, the takeup eyelet, and to the needle. The thread-clutching device 240 is circumvented in the arrangement of FIG. 8 so that at each upstroke of the takeup, the thread is subjected twice inseriatim to the influence of the takeup. By adjusting the position of the bell crank lever 224, the effect of the takeup lever on the first limb of thread directed thereover may be regulated thus to vary the total takeup action on the thread.

Having set forth the nature of this invention, what is claimed herein is:

1. A lockstitch sewing machine having an endwise reciprocatory thread carrying needle, mechanism including a loop taker cooperating with said needle in the formation of lockstitches, and a needle thread takeup means partaking of recurring motion in timed relation with reciprocation of said needle, and means cooperating with said takeup member for manipulating a needle thread in the production of lockstitches having controlled surplus slack thread therein, said means comprising a thread-tensioning device for resisting passage of a thread from a source of supply to said needle, thread-guiding means for directing two successive lengths of said thread extending between said thread-tensioning device and said needle to the influence of said thread takeup means, and a nipper acting on said thread between said two successive lengths thereof and effective to prevent retrograde movement of said thread from said length entering to said needle to said length extending to said thread-tensioning device.

2. A lockstitch sewing machine as set forth in claim 1 in which said thread-guiding means leads a first length of said thread extending from said thread-tensioning device to said nipper across said path of recurring motion of said takeup means for influence by said takeup means during only a portion of each recurring motion thereof, and in which said second length of said thread extending from said nipper to said needle is directed so as to provide for continuous influence by said takeup means.

3. A lockstitch sewing machine as set forth in claim 2 in which a support is provided shiftably sustaining said threadguiding means for directing said first length of thread relatively to said recurring path of motion of said takeup means, and an operator influenced regulator for shifting said thread-guiding means support to vary the portion of said takeup means recurring motion during which said first length of thread is influenced thereby.

4. A lockstitch sewing machine as set forth in claim 1 in which said takeup means includes a reciprocating takeup lever formed with a thread eyelet, in which said thread-guiding means leads a first length of said thread extending from said thread-tensioning device to said nipper across the path of reciprocation of said takeup lever remote from said thread eyelet, and in which said thread-guiding means leads to a second length of said thread extending from said nipper to said needle through said thread eyelet.

5. A lockstitch sewing machine as set forth in claim 4 in which said path of motion of said takeup means provides for an alternate drawing in and paying out of a thread loop of said second length of thread by said thread eyelet, and in which said thread-guiding means positions said first length of thread across that portion of said path of reciprocation of said takeup lever as to cause a drawing in of said first length of thread by said takeup lever while said second length of thread is being paid out by said thread eyelet.

6. A lockstitch sewing machine as set forth in claim 4 in which said path of motion of said takeup means provides for an alternate drawing in and paying out of a thread loop of said second length of thread by said thread eyelet, and in which said thread-guiding mean positions said first length of thread across that portion of said path of reciprocation of said takeup lever as to cause a drawing in of said first length of thread by said takeup lever while said second length of thread is being drawn in by said thread guide.

7. A lockstitch sewing machine as set forth in claim 1 in which said nipper comprises a lever formed with a thread guide notch adjacent each extremity for directing said thread along one side of said lever, a fulcrum for said lever between said extremities, and abutment means fixed relatively to said lever and located adjacent to that side of lever along which said thread is directed by said thread guide notches for engagement with said thread between said fulcrum and a thread guide notch at one extremity of said lever.

8. A lockstitch sewing machine as set forth in claim 1 in which a check spring is arranged to influence that one of said two successive lengths of said thread directed by said threadguiding means which extends to said needle.

9. A lockstitch sewing machine as set forth in claim 1 in which a thread carrying bobbin is arranged in said loop taker and in which a bobbin thread pulloff device is provided for slackening a thread carried by said bobbin during each reciprocation of said needle.

10. A lockstitch sewing machine as set forth in claim 9 in which said mechanism cooperating with said needle in the formation of stitches includes a work feeding dog reciprocated alternately into and out of engagement with a work fabric being stitched and in which said bobbin thread pulloff device comprises a bobbin thread engaging element secured on said work feeding dog and positioned so as to engage and slacken said bobbin thread during each reciprocation of said work feed dog into engagement with a work fabric.

Ill. A thread-controlling device for a lockstitch sewing machine having an endwise reciprocatory needle, a needle thread takeup lever oscillated in timed relation with said reciprocatory needle, a conventional thread-tensioning device with a check spring and thread guide means for directing a thread from said check spring by way of takeup lever to said needle, said thread-controlling device including an attachment to said conventional sewing machine arrangement comprising a support plate attachable to said sewing machine adjacent to said takeup lever, an auxiliary thread-tensioning device carried by said support plate, a thread nipping device carried by said support plate and having a thread inlet, a thread outlet, and means for permitting movement of a thread therethrough in only a direction from. said thread inlet to said thread outlet, thread guide means carried on said support plate for directing a thread between said auxiliary thread-tensioning device and said thread nipping device inlet, and means for securing said supporting plate on a sewing machine with the thread outlet of said thread nipping device located on the same side of the path of oscillation of said takeup lever as said conventional thread-tensioning device and with said thread guide means arranged to direct thread extending from said auxiliary thread-tensioning device across the path of oscillation of said sewing machine takeup lever and to said thread nipping device.

Claims

1. A lockstitch sewing machine having an endwise reciprocatory thread carrying needle, mechanism including a loop taker cooperating with said needle in the formation of lockstitches, and a needle thread takeup means partaking of recurring motion in timed relation with reciprocation of said needle, and means cooperating with said takeup member for manipulating a needle thread in the production of lockstitches having controlled surplus slack thread therein, said means comprising a threadtensioning device for resisting passage of a thread from a source of supply to said needle, thread-guiding means for directing two successive lengths of said thread extending between said threadtensioning device and said needle to the influence of said thread takeup means, and a nipper acting on said thread between said two successive lengths thereof and effective to prevent retrograde movement of said thread from said length entering to said needle to said length extending to said thread-tensioning device.

3. A lockstitch sewing machine as set forth in claim 2 in which a support is provided shiftably sustaining said thread-guiding means for directing said first length of thread relatively to said recurring path of motion of said takeup means, and an operator influenced regulator for shifting said thread-guiding means support to vary the portion of said takeup means recurring motion during which said first length of thread is influenced thereby.

8. A lockstitch sewing machine as set forth in claim 1 in which a check spring is arranged to influence that one of said two successive lengths of said thread directed by said thread-guiding means which extends to said needle.

11. A thread-controlling device for a lockstitch sewing machine having an endwise reciprocatory needle, a needle thread takeup lever oscillated in timed relation with said reciprocatory needle, a conventional thread-tensioning device with a check spring and thread guide means for directing a thread from said check spring by way of takeup lever to said needle, said thread-controlling device including an attachment to said conventional sewing machine arrangement comprising a support plate attachable to said sewing machine adjacent to said takeup lever, an auxiliary thread-tensioning device carried by said support plate, a thread nipping device carried by said support plate and having a thread inlet, a thread outlet, and means for permitting movement of a thread therethrough in only a direction from said thread inlet to said thread outlet, thread guide means carried on said support plate for directing a thread between said auxiliary thread-tensioning device and said thread nipping device inlet, and means for securing said supporting plate on a sewing machine with the thread outlet of said thread nipping device located on the same side of the path of oscillation of said takeup lever as said conventional thread-tensioning device and with said thread guide means arranged to direct thread extending from said auxiliary thread-tensioning device across the path of oscillation of said sewing machine takeup lever and to said thread nipping device.