US3628481A

US3628481A - Automatic looper thread control mechanism for chainstitch sewing machines

Info

Publication number: US3628481A
Application number: US36333A
Authority: US
Inventors: Helmut Gross
Original assignee: GM Pfaff AG
Current assignee: GM Pfaff AG
Priority date: 1969-05-13
Filing date: 1970-05-11
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21
Also published as: DE1924283B1

Abstract

In a double-chainstitch sewing machine having a reciprocatory needle, a thread-carrying oscillating looper, a work feed dog, a stitch controller and an oscillating looper thread takeup lever, the amount of looper thread withdrawn by the takeup lever during a stitching cycle is automatically varied in direct proportion to the stitching length. For this purpose, the takeup lever is operated via a pair of oscillating drives to impart thereto a basic and constant amplitude oscillating movement in one direction from a zero reference position, corresponding to a minimum stitching length, said basic oscillating movement having superimposed thereon an additional oscillating movement increasing in amplitude as the stitching length is increased. The basic oscillating movement of the takeup lever is derived from the main drive shaft of the machine via an eccentric and the additional oscillating movement of the lever is derived, via drive means including a knuckle joint, from the rockshaft of the machine oscillating at varying amplitudes in accordance with the adjustment of the stitch controller and controlling the feed dog displacement in the direction parallel to the sewing direction.

Description

i United States Patent Inventor Appl. No.

Filed Patented Assignee Priority I-Ielmut Gross Kaiserslautern/Ptalz, Germany 36,333

May 11, 1970 Dec. 21,1971

G. M. Plait AG Kaiserslautern/Pfalz, Germany May 13, 1969 Germany AUTOMATIC LOOPER THREAD CONTROL MECHANISM FOR CHAINSTITCH SEWING MACHINES 8 Claims, 4 Drawing Figs.

Primary ExaminerH. Hampton Hunter Attorney-Greene & Durr ABSTRACT: In a double-chainstitch sewing machine having a reciprocatory needle, a thread-carrying oscillating looper, a work feed dog, a stitch controller and an oscillating looper thread takeup lever, the amount of looper thread withdrawn by the takeup lever during a stitching cycle is automatically varied in direct proportion to the stitching length. For this purpose, the takeup lever is operated via a pair of oscillating drives to impart thereto a basic and constant amplitude oscillating movement in one direction from a zero reference position, corresponding to a minimum stitching length, said basic oscillating movement having superimposed thereon an additional oscillating movement increasing in amplitude as the stitching length is increased. The basic oscillating movement of the takeup lever is derived from the main drive shaft of the machine via an eccentric and the additional oscillating movement of the lever is derived, via drive means including a knuckle joint, from the rockshaft of the machine oscillating at varying amplitudes in accordance with the adjustment of the stitch controller and controlling the feed dog displacement in the direction parallel to the sewing direction.

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PATENTED UECZI 1971 3523 4531 SHEET 2 OF 2 IiNVENTOR HEt/VW 4300 4 rmuz'r AUTOMATIC LOOPER THREAD CONTROL MECHANISM FOR CHAINSTITCH SEWING MACHINES The present invention relates to double-chainstitch sewing machines including a thread-carrying oscillating looper, an adjustable stitch controller, to vary the stitching length, and a looper thread takeup lever, the major object of the invention being the provision of control mechanism to automatically vary the amount of looper thread withdrawn by said lever in direct proportion to the stitching length.

in double-chainstitch sewing machines, in particular those of the type having a loop taker or looper oscillating in a direction parallel to the work feed or sewing direction, control of the looper thread supply is effected generally be means of a looper thread takeup lever oscillating between a pair of stationery thread guides, as well as by the movement of the looper itself, although the effect of the latter on the thread takeup is rather limited. Both the looper and thread takeup lever are operated via eccentric devices, whereby the oscillating movements are of constant amplitude.

Inasmuch as the length of looper thread required for a single chainstitch formation is equal to about three times the stitching length, an insufficient amount of loose looper thread is available as the stitching length increases on account of the constant oscillating movement of the takeup lever, resulting thereby in a distortion of contraction of the stitches, on the one hand, while leaving a substantial amount of excess thread or resulting in lack of stitch tightness as the stitching length is decreased, such for instance as in the case of sewing barring stitches at the end of a seam, on the other hand.

In view of the foregoing defects it is necessary, in the case of relatively great stitching length changes, to account for the varying demand of looper thread as a function of the stitching length by a readjustment of the takeup lever, such as by a variation of the effective leverage and corresponding adaptation of the thread guides.

Where the oscillation of the looper thread takeup lever is derived from an eccentric mounted upon the main drive shaft of the machine, a variation of the effective leverage results in an increased or decreased deflection of the takeup lever equally in both directions from a zero reference plane containing the thread guides, whereby to prevent utilization to the full extent of the deflection of the lever for the withdrawal of looper thread from its supply spool. Besides, readjustments of the takeup lever control elements, to ensure proper and reliable stitch formation, are both time consuming and may be made only with the machine being at rest and by specially trained personnel.

in an effort to avoid manual readjustments when changing from one stitching length to another, it has already been proposed to adjust the looper thread control lever simultaneously with the setting of the stitching length by a conventional stitch controller.

According to a known arrangement of the latter type, it is proposed to vary, simultaneously with the displacement of a link controlling the stroke of the work feed dog, the mutual distance between a fork-shaped thread guide and a threadwithdrawing finger having an arcuate thread-withdrawing surface and oscillating in synchronism with the looper rockshaft. There is required in this case, in addition to the threadwithdrawing finger and for the takeup of the excess thread during the loop-shedding movement of the looper, a special thread takeup member also being oscillated by the looper rockshaft and acting upon the looper thread via two further thread guides, to maintain a constant thread supply for all stitching lengths. Both control devices are mounted upon the looper rockshaft and act simultaneously upon the looper thread. In order to ensure proper control of the looper thread in relation to the looper movement, it is furthermore necessary to provide a controllable thread clamp between the two devices to take up and withdraw respectively different amounts of thread. Due to the mounting of the thread control devices and of the thread clamp upon the looper rockshaft, the mass of the latter is increased considerably, whereby to make it practically impossible to achieve the high-operating speeds required in present'day sewing machines equipped in this manner. Besides, with machines of this type the adjustment of the work feed dog and in turn of the thread control elements can be carried out only while the machine is at rest, quite aside from the fact that, due to the relative displacement of the stationary thread guide and the arcuate withdrawing finger, the beginning and end of the thread withdrawal are varied simultaneously, substantially without any effect on the looper movement which latter remains substantially constant. As a consequence, the thread control is highly unreliable and inaccurate in arrangements of this type.

A further known looper thread control device comprises a thread takeup lever arranged to oscillate between stationary thread guides and secured to an end of a two-arm lever which is rotatively mounted, approximately .at the center of its arms, upon a supporting lever rotatable about a stationary axis. One of the lever arms is operably connected, via a pull rod with an eccentric driving the thread takeup, while the other lever arm is connected via a link with an extension of an eccentric rod embracing the work feed eccentric, said rod serving to operate, via a slide block and guide mechanism, an oscillating lever transmitting oscillating movement to the work feed dog of the machine.

The drive of the takeup lever is, in a device of the foregoing type, constructed in such a manner that, during variations of the stitching length, both the extent and the position of the oscillating movement of the thread takeup lever, as related to a horizontal reference plane containing the thread guides, are varied in such a manner that the oscillating movement in case of a relatively great stitching length occurs essentially below said plane and are somewhat less than in case of a short stitching length, whereas in case of a relatively short stitching length said movements occur essentially above said plane and are somewhat greater than in the case of a great stitching length, respectively.

As a consequence, the thread takeup lever in cooperation with a thread clamp, in turn controlled in dependence upon the stitching length, operates predominantly as a threadwithdrawing means in the case of greater stitching lengths, on the one hand, and as a thread takeup means in the case of the shorter stitching lengths, on the other hand. Control mechanism depending upon the stitching length of this typewhich applies specifically to sewing machines having a hookshaped and eye-pointed needle disposed side by side below the cloth plate and operating by the thread loop transferred upwardly through the fabric by the eye-pointed needle being brought within the operating range of the hook-shaped needle during the return stroke of the eye-pointed-needle takes however no account of the conditions obtaining with sewing machines having an oscillating looper, that is, where the same amount of loose thread must be taken up during the return movement of the loop taker independently of the stitching length, on the one hand, and where varying amounts of thread must be withdrawn from the thread supply depending upon the stitching length, on the other hand.

In brief, the previous attempts to achieve an automatic looper thread control in chainstitch sewing machines have resulted in both highly complex mechanisms as well as limited accuracy of the control, or are limited to specific machine designs, whereby to render the known devices unsuited for most practical purposes, especially for use in present day highspeed sewing machines having an oscillating loop taker.

Accordingly, an important object of the present invention is to eliminate or minimize the foregoing and related drawbacks and difficulties encountered with previous looper thread control devices for chainstitch sewing machines.

A more specific object of the invention is to dispense with any manual readjustment of the looper thread guide and control elements when changing from one to another stitching length.

Yet another object of the invention is the provision of means, in conjunction with double-chainstitch sewing machines of the referred to type, to vary, in dependence of the stitching length, the stroke of the looper thread takeup lever oscillating between a pair of stationary thread guides, to provide the exact amount of required looper thread for the sewing of any stitching length set by the stitch controller.

The invention, both as to the foregoing and ancillary objects as well as novel aspect thereof, will be better understood from the following detailed description, taken in conjunction with the accompanying drawings forming part of this disclosure and in which:

FIG. 1 is a front view of a double-chainstitch sewing machine, shown with the parts mounted below the cloth plate of the machine uncovered and embodying automatic looper thread control mechanism constructed in accordance with the principles of the invention;

FIG. 2 is a partial perspective view more clearly illustrating the parts below the cloth plate of the machine of FIG. 1 and their cooperation is effecting automatic looper thread control according to the invention;

FIG. 3 is a diagram explanatory of the function and operation of the improved looper thread takeup control; and

FIG. 4 is a partial perspective view explanatory of the stitch formation by the machine according to the preceding figures.

Like reference numerals denote like parts in the different views of the drawings.

With the foregoing objects in view, the invention involves generally the provision of a pair of drive means for the operation of the looper thread takeup lever, to impart thereto a composite oscillating movement in a predetermined direction from a reference plane or position, said movement being composed of a first constant-amplitude component and a second component superimposed upon the first component and varyin g in direct proportion to the stitching length.

According to a constructionally simple solution to produce the composite movement of the thread takeup lever, the drive mechanism of said lever comprises a pair of motion-transmitting paths one of which includes a first level operated with a constant oscillating amplitude and linked to the corner point of an intermediate angular lever having one arm operably connected with the thread takeup lever, while the other transmitting path includes a second lever operably connnected with the horizontal oscillating drive means of the feed dog, on the one hand, and connected via a link to the remaining arm of said angular lever, on the other hand, said second lever and link forming a knuckle joint designed to assume a substantially stretched position when the thread takeup lever passed through its zero oscillating or reference position, in a manner as will become more apparent as the description proceeds in reference to the drawings.

Referring more particularly to FIG. 1, the same shows a conventional double-chainstitch sewing machine with combined lower and upper feed, comprising a frame or cloth plate 1 supporting a housing 2 being constituted by the usual upright and overhanging arm parallel to said plate and terminating in a sewing head 3. Rotatively mounted in the housing 2 is the main drive or arm shaft 4 rotated in a known manner by a drive motor (not shown). Shaft 4 carries a hand wheel 5 at one end and serves to drive, via a crank 6, link 7 and pin 8 disposed at the opposite end of the shaft, the needle bar mounted for vertical reciprocation in the needle bar frame 9 which is in turn mounted in the head 3 for oscillation in the feed or sewing direction. Needle bar 10 carries the sewing needle 11 at the lower end thereof. The drive shaft 4 is furthermore operably connected, via a chain belt 12 and a first chain wheel 13 upon said shaft, with an auxiliary drive shaft 14 rotatively mounted below the plate 1 and carrying a cooperating chain wheel 15 engaged by said belt.

Secured to the shaft 14 is a work feed eccentric 16, FIG. 2, which serves to drive an oscillating push bar 22 via an eccentric rod 17, a double-arm oscillating lever 18 rotatively mounted about a pivot 19 fast upon the plate 1 and having a lever arm provided with an arcuate guide slot 20 in which is displaceably disposed a slide block 21 linked to one end of the rod 22. Linked to the opposite end of the rod 22 is a crank 23 being secured to one end of a rockshaft 24 parallel to the shaft 14 and rotatively mounted in the frame of the machine. Secured to the opposite end of the rockshaft 24 is a further crank 25 linked to a work feed dog 26.

The rockshaft 24, being driven by the auxiliary shaft 14 via the transmission means described in the foregoing, serves to impart to the feed dog 26 a horizontal component oscillating movement in the direction of and opposite to the feed direction of the sewing machine. The extent of this movement and in turn the horizontal feed stroke of the dog 26 or stitching length of the machine, may be adjusted by the setting of a stitch control lever 27 operably connected, via a link 28, with the push bar 22. The front end of the stitch control lever 27 rotatively mounted at its opposite end in the housing 2 passed through a slit 29 of said housing, FIG. 1, and is fitted with a setscrew 30 to fix a desired feed stroke or stitching length. A tension spring 31 having one end secured to the housing 2 and having its opposite hook-shaped end engaging a bore in the bar 22 serves to hold the stitch controller in the position determined by the adjusting position of the screw 30. The farther the guide block 21 is displaced from the pivot pin 19, the greater will be the oscillating movement imparted to the rockshaft 24 by the rod 22 and the greater will be the horizontal operating stroke of the dog 26 and in turn the stitching length.

In order to produce vertical oscillating movements of the feed dog 26, there is provided a further eccentric 32 mounted upon shaft 14 and operably connected with the dog 26 via an eccentric rod 33, a first crank 35 secured to an intermediate shaft 34 journaled in the frame 1, a second crank 36 secured to shaft 34 and a line 38 connecting the crank 36 with a lever arm 37 of the feed dog 26. Both horizontal and vertical oscillating component movements imparted to the dog 26 by the eccentrics l6 and 32 result in the well-known four-motion composite feed movement well known in connection with conventional sewing machines.

In the example illustrated, the lower work feed by the dog 26 is supplemented by an upper feed by the needle 11 carrying out, aside from its vertical reciprocation for the stitch formation, oscillating movements in the feed direction and in synchronism with the horizontal feed movements of the dog 26. In order to cause the feed stroke of the needle 11 to equal the feed stroke of the feed dog 26, rockshaft 24 has secured to it a crank 39, FIG. 1, to which is linked the lower end of a vertical connecting rod 40 whose opposite end is linked to a crank 41. The latter is secured to a further rockshaft 42 mounted in the am of the housing 2. Secured to the end of the rockshaft 42 extending into the head 3 is a further crank 43 carrying a pin 44 which engages a guide slot 45 in the needle bar supporting frame 9. As a consequence, both the needle 1 l and feed dog 12 are subjected to equal and synchronous oscillating movements in the work feed direction having a stroke adjustable by the aid of the stitch controller in the manner described.

The looper mechanism comprises a support 46, FIG. 1, carrying the looper proper 47 mounted for oscillation in the direction parallel to the feed direction about a shaft 48 journaled in the frame 1 and below shaft 14, support 46 being secured against axial displacement by a pair of setting rings only one of which (49) is shown in FIG. 1. Looper support 46 has a lever arm 50 to which is linked the eccentric rod 51 of an eccentric 52 mounted upon 14, auxiliary drive shaft 14, to provide operating drive movement for the loop taker 47.

Cooperating with the looper 47 is a loop spreader 53, FIG. 1, secured to the end of a push bar 54 mounted upon the frame 1 for oscillation in the direction transverse to the work feed direction. Push bar 54 is operated by a further eccentric 55, secured to the auxiliary shaft 14, via an eccentric rod 56, a bellcrank level 58 disposed upon a crank shaft 57 and a link 59 connecting lever 58 with bar 54.

The looper thread control mechanism comprises a thread takeup or withdrawing lever 60, FIG. 2, having a flat angularly bent end portion 61 provided with a thread guide bore 62 and projecting into the space enclosed by the legs 63 of a stationary Ueshaped thread guide 64, both said legs being provided with further thread 'guide bores 65 normally registering with and cooperating with the guide bore 62 in the manner more clearly described and explained in the following. The thread guide 64 is adjustably mounted upon the frame 1 by means of a setscrew 67 engaging a slot 66 of said guide.

The thread takeup lever 60 is adjustably secured to a rockshaft 68 joumaled in the frame 1 about an axis parallel to the work feed direction, shaft 68 being linked, via a crank 69 and link 70, to the arm 71 of an angular intermediate lever 73 having a pair of lever arms 71 and 72. The angular lever 73 is operated by two different drives derived respectively from an eccentric 74 mounted upon the continuously rotating shaft 14 and a crank 81 mounted upon the rockshaft 24. For this purpose, eccentric 74 is connected to the angular Lever 73 via an eccentric rod 75 and a bellcrank lever 76 rotatively mounted upon the shaft 24 and having a first lever arm 77 linked to the eccentric rod 75 by a pin 79 and a second lever arm 78 linked by a pin 80 to the corner of the angular lever 73, while crank 81 is connected to the arm 72 of the lever 73 via an intermediate link 82 and pivot pins 83 and 84, respectively, in such a manner that crank 81 and link 82 form a knuckle joint designed and operating in the manner described and explained in greater detail in the following.

Design and adjustment of the parts described in the foregoing is such that in the zero position of the thread takeup lever 60, in which the thread guide bores 62, 65 of the lever and of the guide 64 are in register, as shown in FIG. 2, the crank 81 and link 82 forming the knuckle joint approximately assume their stretched position, as shown in both FIGS. 2 and 3.

The looper thread 85, FIG. 1, is passed from its supply spool 86 and via an eyelet guide 87, a thread-tensioning device 88, a pair of further thread guides 89 and 90, the thread guide bores 62 and 65 of the takeup and two further eyelet guides 91 and 92, to the looper 47 and through the guide bores of the latter, FIG. 4, in a manner well known in connection with chainstitch sewing machines with oscillating looper.

The needle thread 93 is passed form its supply spool 94 to the eye of the needle 11 via a tensioning device 95, eyelet guide 96 and a thread takeup 97 mounted upon the needle bar 10, both the needle and looper threads cooperate with the remaining stitch-forming tools in a known manner, to produce chainstitches in the work operated on, as illustrated in FIG. 4.

In operation, rotation of the drive shaft 4 imparts vertical reciprocating movements to the needle bar and in turn to the needle 11 via crank 6, link 7 and pin 8 and at the same time rotational movement to the auxiliary drive shaft 14 via the chain wheels 13, 15 and belt 12, shaft 14 c carrying the driving

eccentrics

16, 32, 52, 55 and 74. This in turn results in the rockshaft 24 being subjected to oscillating movements via the eccentric 16, eccentric rod 17, oscillating lever 18, slide block 21 within guide slot 20, push bar 22 and crank 23, the oscillating movements of shaft 24 being transmitted to the feed dog 26 via crank 25, to reciprocate said dog in the horizontal work feed direction.

At the same time, the needle bar frame 9 and in turn the needle bar 10 carrying the needle 11 are subjected to oscillating movements in the feed direction with the same feed stroke or amplitude as the dog 26 and transmitted via the crank 39 upon the shaft 34, connecting rod 40, crank 41, rockshaft 42, oscillating crank 43 and pin 44. The oscillating amplitudes of the feed dog 26 and of the frame 9 may be adjusted gradually and simultaneously by varying the position of the slide block 21 within the guide slot of the lever 18 of the

stitch controller

27, 30.

Further imparted to the feed dog 26 and in proper time phase relation to its horizontal oscillating component is a vertical oscillating component derived from the eccentric 32 via the eccentric rod 33, cranks 35 and 36 upon the intermediate shaft 34 and link 38, to cause the dog 26 to carry out quadrilateral feed movements in synchronism with the needle feed and reciprocating movements, in a manner well known in the operation of sewing machines having a combined lower and upper feed.

Oscillating movements of the looper 47 in a direction parallel to the feed direction and in synchronism with the needle reciprocations, to produce double chainstitches in cooperation with the needle 11 in the work being operated on, FIG. 4, with the looper 47 secured to the support 46 with its beak pointing in a direction opposite to the feed direction, is derived from the eccentric 52 via the eccentric rod 51 linked to the lever arm 50 of the looper support 46.

Cooperating with the looper 46 is the loop spreader 53 carried by the push bar 54 and being periodically displaced or oscillated, transversely to the feed direction, via the eccentric 55, eccentric rod 56, bellcrank lever 58 and link 59 connecting the bar 54 with said lever, spreader 53 operating in known manner to seize, during the loop-shedding movements of the looper 47 in the feed direction, the looper thread above and between the guide bore in the looper and the last stitch in the work, to form a so-called thread triangle transversed by the needle during a stitch-forming cycle.

Starting from the position of the parts shown in the drawings, that is, with the work feed in the forward direction having just been completed, with the needle 11 leaving the work or fabric during its upward oscillating stroke, with the feed dog 26 having completed its forward stroke and commencing its downward movement away from the work, with the looper 47 having entered the needle thread loop, with the spreader 53 being positioned to the left of the looper as viewed by the operator, with the looper thread takeup lever 60 being in the zero position in which the axes of the guide bores are in registry with each other, and with the arms 81 and 82 of the knuckle joint assuming approximately their stretched position, the looper thread 85 is controlled during an operating or stitching cycle as follows.

While the looper 47, during the upward and simultaneous oscillating movement of the needle in the direction opposite to the feed direction, at first still moves opposite to the feed direction until being reversed upon reaching the rear dead end position, the thread takeup lever 60, positioned between the legs of the thread guide 63 and driven by the eccentric 74 via the eccentric rod 75, angular lever '76 rotatively mounted upon shaft 24, angular lever 73, link 71) and crank 69 secured to rockshaft 68, is displaced in the downward direction, whereby to at first take up the loose looper thread resulting from the return stroke of the looper 47 and to thereafter tension said thread, to in turn result, during movement of the spreader 53 toward the right as viewed by the operator and seizure thereby of the looper thread and drawing out of the latter to the thread triangle between the guide bore of the looper the work and needle thread loop, in the withdrawal from the spool 86 of the amount of thread 85 necessary for a stitch formation. As soon as the needle: again enters the work, the takeup lever 60 is at its greatest distance from the guide bores 65, this position of the lever coinciding with the commencement of the forward feed stroke of both the needle 11 and feed dog 26.

During the forward feed stroke, with the needle penetrating the thread triangle, with the spreader 53 moving towards the left as viewed by the operator, to release the looper thread, and with the looper 47 shedding the needle thread loop tensioned by the upward movement of the: needle and the needle thread takeup to result in the tightening of the needle thread loop against the underside of the work, FIG, 4 and, furthermore, during the oscillating movement of the looper 47 in the direction opposite to the feed direction and following the shedding of the needle thread loop, the thread takeup lever returns to its zero position shown in the drawing, whereby to release the previously slightly tensioned thread and to thereby maintain the looper thread in tensioned condition during the formation of the thread triangle and takeup of the needle thread loop by the looper, on the one hand, and to take into account the thread consumption by the takeup during the forward feed stroke, on the other hand.

As the needle 11 emerged from the work, the work feed is completed and the takeup lever 60 has again reached its zero position in which it will remain briefly, while the arms 81 and 82 of the knuckle joint pass through the stretched position, whereupon the takeup lever 60 is again deflected in the downward direction with upgoing needle, for the commencement of a new stitch formation, between the legs 63 of the thread guide 64.

The mechanism effecting looper thread control is preferably so designed that with a short of minimum stitching length, corresponding to the minimum spacing distance between the slide block 21 from the pivot 19 of the stitch controller, the deflection a, FIG. 3, of the takeup lever 60 is controlled essentially by the eccentric 74 and the position of angular lever 76 and is not or only slightly affected by the position of the arms 81, 82 of the knuckle joint.

If now the distance of the slide block 21 within the slot 20 of the oscillating lever 18 from the pivot 19 of the stitch controller is increased through adjustment of the lever 27, the oscillating amplitude of the rockshaft 24 is increased via the respective transmission means between said shaft and the auxiliary drive shaft 14, whereby an increased feed movement is imparted to both the feed dog 26 and the needle bar 10, to result in a correspondingly increased stitching length. The increase of the amplitudes of the dog 26 and bar are uniform in both oscillating directions.

In addition to the constant oscillating component of the takeup lever 60 derived from the eccentric 74 and imparted thereto by the angular lever 76 operated at a constant oscillating amplitude, as described in the foregoing, the thread takeup lever 60 has imparted to it an additional unidirectional oscillating or deflecting movement via the crank or lever 81, mounted upon the rockshaft 24 and oscillating with varying amplitude in accordance with the stitching length as adjusted by the stitch controller, and link 82 of the knuckle joint connecting crank 81 with the lower arm 72 of the angular lever 73.

The increase of the oscillating amplitude of the rockshaft 24 resulting from an increase of the stitching length by adjustment of the stitch controller, which amplitude increase occurs uniformly in both oscillating directions of said shaft, is not or only to an negligible extent transmitted, during deflection of the lever 81 in the upward direction, in the example illustrated, to the angular lever 73 and in turn to the takeup lever 60. On the other hand, during deflection of the lever 81 in the downward direction the same assumes with the link 82 a relatively bent position, in such a manner as to reduce the distance between the shaft 24 and the pivot 84 of the angular lever 73 and to rotate the latter about its pivot 80. As a consequence, provision and proper design of the knuckle joint 81, 82 in relation to the remaining transmitting elements, in the manner shown and described, has the effect of superimposing the oscillating movements of lever 81, varying in proportion to the stitching length, upon the constant deflection a of the takeup lever 60 in a single direction only, as indicated by b in FIG. 3.

In brief, the invention, provides a proper basic adjustment of the thread takeup control elements for a normal or minimum stitching length, in the manner described, substantially dispenses with any manual readjustment of said elements as the stitching length is increased by means of the stitch controller, because of the provision and function of the knuckle joint 81, 82 causing the amplitude increase of the oscillations of the rockshaft 24, increasing with the stitching length and occurring uniformly in both oscillating directions of said shaft, to be imparted to the takeup'lever 60 in a single oscillating direction only of said lever, the amplitude increase in the opposite oscillating direction being taken up by the knuckle joint. In other words, the knuckle joint has the effect that the oscillating amplitude or deflection of the takeup lever 60 is increased, starting a basic or minimum amplitude, in the downward direction only in respect to the reference plane containing the thread guide bores 65 in the example illustrated. The result is an automatic increase of the thread withdrawal in proportion to increases of the stitching length beyond a minimum or normal value.

There is furthermore ensured by the invention that the takeup of loose looper thread, the thread withdrawal in proportion to the stitching length and the thread takeup at all stitching lengths always occur at the same time phase position within a stitch formation or cycle, on the one hand, and that there is substantially prevented thereby a deflection of the takeup lever 60 in the opposite (upward) direction followed by an increase of the stitching length, such upward deflection being liable to unfavorably affect the chainstitch seam being sewn by undesired withdrawal and/or tensioning of the looper thread, at improper points within a stitching cycle on the other hand.

Looked at in a different way, the knuckle joint 81, 82 acts as a limit or clipper in eliminating the effect of one of the alternations or halfway oscillations of the shaft 24, varying in amplitude in proportion to the stitching length, on the takeup lever 60, to substantially suppress or minimize deflection of the latter in a direction opposite to its normal or threadwithdrawing (downward) deflections and to result in an accurate and reliable looper thread withdrawal increasing in direct proportion to the stitching length, in the manner described hereinbefore.

While a sewing machine with combined lower and upper feed is shown by the drawings, it is understood that the invention applies with equal advantage to machines having a single feed only, such as by the omission of the needle oscillating frame 9 and its associated operating means.

In the foregoing, the invention has been described in reference to a preferred exemplary device or embodiment It will be evident, however, that variations and modifications, as well as the substitution of equivalent parts or devices for those shown herein for illustration, may be made in accordance with the broader scope and spirit of the invention.

1 claim:

1. In a chainstitch sewing machine including a thread-carrying reciprocatory needle, a thread-carrying looper and a work feed dog mounted for oscillation in the feed direction, to determine the length of the stitches formed by said needle in cooperation with said looper, the combination comprising;

1. a continuously running drive shaft with means to operate said needle thereby,

2. a rockshaft to operate said feed dog,

3. motion-transmitting means operably connecting said rockshaft with said drive shaft,

4. a stitch controller operably associated with said motiontransmitting means, to adjust the feed stroke of said dog,

5. a looper thread takeup lever, to supply a predetermined amount of loose looper thread during a stitching cycle,

and

6. a pair of drive means for said takeup lever to apply thereto a first oscillating component movement, in respect to a zero position, having a constant amplitude corresponding to a predetermined stitching length, and a second unidirectional oscillating component movement superimposed upon said first oscillating movement and increasing in amplitude from substantially zero in proportion to the stitching length increase by said controller beyond said predetermined stitching length.

2. In a chainstitch sewing machine as claimed in claim 1, wherein said first oscillating component movement of said takeup lever is derived from said drive shaft via an eccentric and said second component oscillating movement of said takeup lever is derived from said rockshaft via a knuckle joint having a substantially stitched position coinciding with the position of said takeup lever.

3. In a chainstitch sewing machine as claimed in claim 1, wherein said first and second oscillating component movements are applied to said takeup lever via an angular lever having a pair of lever arms and a free pivot at the corner thereof, an eccentric secured to said drive shaft, first motiontransmitting means operably connecting one arm of said angular lever with said takeup lever, second motion-transmitting means operably connecting said pivot with said eccentric, and a knuckle joint having a first arm secured to said rockshaft and a second arm linked to the remaining arm of said angular lever, said knuckle joint having a stretched position approximately coinciding with the zero position of said takeup lever,

4. In a chainstitch sewing machine as claimed in claim 1, wherein said predetermined stitching length corresponds to the minimum stitching length adjustable by said stitch controller and said drive means for said takeup lever is designed so as to result in an increase of the looper thread supply in direct proportion to the stitching length increase beyond said minimum stitching length.

5. In a chainstitch sewing machine including a cloth plate, a vertically reciprocable thread-carrying needle mounted above said plate, a thread-carrying oscillating looper mounted below said plate, and a work feed dog mounted in said plate for oscillation in the feed direction, to determine the length of the stitches formed by said needle in cooperation with said looper, the combination comprising:

1. a continuously running drive shaft above said plate with means to operate said needle thereby, 2. an auxiliary drive shaft below said plate with means to 'drive the same by said drive shaft,

3. a rockshaft below said plate to operate said feed dog,

4. motion-transmitting and converting means connecting said rockshaft with said auxiliary drive shaft,

5. a stitch controller operably associated with said motiontransmitting means, to adjust the feed stroke of said dog,

6. a looper thread takeup lever, to supply a predetermined amount of loose looper thread during a stitching cycle, and

7. a pair of drive means for said takeup lever to apply thereto respectively a first unidirectional oscillating movement in respect to a zero position derived from said auxiliary drive shaft, said first oscillating movement having a constant amplitude corresponding to a predetermined stitching length, and a second unidirectional component oscillating movement derived from said rockshaft in phase with and superimposed upon said first movement, said second oscillating movement increasing in amplitude from substantially zero in proportion to the stitching length increase by said controller beyond said predetermined stitching length.

6. In a chainstitch sewing machine as claimed in claim 5, wherein said predetermined stitching length corresponds to a normal minimum stitching length adjustable by said stitch controller and wherein said drive means for said takeup lever are designed to result in an increase of the looper thread withdrawn by said lever varying in direct proportion to the stitching length increase from said normal length.

7. In a chainstitch sewing machine as claimed in claim 5, including means operably connected to said rockshaft, to operate said needle, in addition to its vertical reciprocation, in the feed direction and in phase synchronism with said feed dog, to provide a combined lower and upper feed of the work operated on.

8. In a chainstitch sewing machine as claimed in claim 5, wherein said first and second oscillating component movements are applied to said takeup lever via a first angular lever having a pair of lever arms and a free pivot at its corner, an eccentric upon said auxiliary drive shaft first motion-transmitting means including a second angular lever rotatively mounted upon said rockshaft and operably connecting said pivot with said eccentric, second motion-transmitting means operably connecting one arm of said first angular lever with said takeup lever, and a knuckle joint having a first arm secured to said rockshaft and a second arm linked to the remaining arm of said angular lever, said knuckle joint having a stretched position approximately coinciding with the zero position of said angular lever,

Claims

1. In a chainstitch sewing machine including a thread-carrying reciprocatory needle, a thread-carrying looper and a work feed dog mounted for oscillation in the feed direction, to determine the length of the stitches formed by said needle in cooperation with said looper, the combination comprising; 1. a continuously running drive shaft with means to operate said needle thereby, 2. a rockshaft to operate said feed dog, 3. motion-transmitting means operably connecting said rockshaft with said drive shaft, 4. a stitch controller operably associated with said motiontransmitting means, to adjust the feed stroke of said dog, 5. a looper thread takeup lever, to supply a predetermined amount of loose looper thread during a stitching cycle, and 6. a pair of drive means for said takeup lever to apply thereto a first oscillating component movement, in respect to a zero position, having a constant amplitude corresponding to a predetermined stitching length, and a second unidirectional oscillating component movement superimposed upon said first oscillating movement and increasing in amplitude from substantially zero in proportion to the stitching length increase by said controller beyond said predetermined stitching length.

2. a rockshaft to operate said feed dog,

2. an auxiliary drive shaft below said plate with means to drive the same by said drive shaft,

3. a rockshaft below said plate to operate said feed dog,

3. In a chainstitch sewing machine as claimed in claim 1, wherein said first and second oscillating component movements are applied to said takeup lever via an angular lever having a pair of lever arms and a free pivot at the corner thereof, an eccentric secured to said drive shaft, first motion-transmitting means operably connecting one arm of said angular lever with said takeup lever, second motion-transmitting means operably connecting said pivot with said eccentric, and a knuckle joint having a first arm secured to said rockshaft and a second arm linked to the remaining arm of said angular lever, said knuckle joint having a stretched position approximately coinciding with the zero position of said takeup lever.

4. a stitch controller operably associated with said motion-transmitting means, to adjust the feed stroke of said dog,

5. a stitch controller operably associated with said motion-transmitting means, to adjust the feed stroke of said dog,

5. a looper thread takeup lever, to supply a predetermined amount of loose looper thread during a stitching cycle, and

8. In a chainstitch sewing machine as claimed in claim 5, wherein said first and second oscillating component movements are applied to said takeup lever via a first angular lever having a pair of lever arms and a free pivot at its corner, an eccentric upon said auxiliary drive shaft first motion-transmitting means including a second angular lever rotatively mounted upon said rockshaft and operably connecting said pivot with said eccentric, second motion-transmitting means operably connecting one arm of said first angular lever with said takeup lever, and a knuckle joint having a first arm secured to said rockshaft and a second arm linked to the remaining arm of said angular lever, said knuckle joint having a stretched position approximately coinciding with the zero position of said angular lever.