US3396688A - Rotary looping device for a sewing machine - Google Patents

Description

13, 1968 YOSHIHXKO NAKAJIMA ETAL. 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Filed July 18, 1966 8 Sheets-Sheet l INVENTOR ym'pia l f 2 BY g wmuz Hw-Q Aug. 13, 1968 YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Filed July 18, 1966 8 Sheets-Sheet 2 INVENTORS Yuma/u aw 1w fife-mu m fi/W 13, 1958 YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Filed July 18, 1966 8 Sheets-Sheet 3 INVENTOR: y -1;; k ,uaka Vnq BY Methane: Ha/Q A /f r/h Aug. 13, 1968 YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE 8 Sheets-Sheet 4 Filed July 18, 1966 INVENTORS 91 4411 80 ela/1m BY kmanam Aug. 13, 1968 YOSHlHl KO NAKAJIMA ETAL.

ROTARY LQOPING DEVICE FOR A SEWING MACHINE 8 Sheets-Sheet 5 Filed July 1. 1966 c5 .Qw a .Q w QQ \|\\\|a T n n Qw 1 l h g I at I I\ III! .53 g H Q Q n au L YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Aug 13, 1968 8 Sheets-Sheet 6 Filed July l8,

INVENTORJ final/; flab/m1 a BY Maw/man 94/22 0440.41 White v my U N\ u A g- 13, 1968 YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Filed July 18, 1966 a Sheets-Sheet 7 P PP Q 8 R T P a" 4 Z i 0' 20'40' was" m 3/0 360' /6 I 1NVENT R5 ww. llle-hj/ne BY Maul/ W4 gm 13, 1 YOSHIHIKO NAKAJIMA ETAL 3,396,688

ROTARY LOOPING DEVICE FOR A SEWING MACHINE Filed July 18, 1966 8 Sheets-Sheet 8 INVENTOR5 yfla'liikp ald fra B Baa/nun Hal-a Malad J 'nlw United States Patent 3,396,688 ROTARY LOOPING DEVICE FOR A SEWING MACHINE Yoshihiko Nakajima and Kazumasa Hara, Tokyo, Japan, assignors to Janome Sewing Machine C0., Inc., Ltd., Tokyo, Japan Continuation-impart of application Ser. No. 536,364, Mar. 22, 1966. This application July 18, 1966, Ser. No. 569,547 Claims priority, application Japan, July 17, 1965, 40/ 43,070 Claims. (Cl. 112-228) ABSTRACT OF THE DISCLOSURE The present invention relates to a rotary looping device for a sewing machine, and more particularly to a looping device in which a rotary hook means holds a bobbin with a thread, and loops an upper thread supplied by the needle of the sewing machine over the lower bobbin thread to form a stitch of the two threads.

Conventional household sewing machines employ oscillating shuttles which turn only 180 so that the inertia of the oscillating shuttle body is not utilized and has to be overcome by the drive means resulting in a noisy and jerky action, preventing the operation of the machine at high speed. Therefore, sewing machines for industrial use are preferably provided with rotary hooks enveloping an inner body. Known rotary hook loop formers are rather complicated, and if any repair or adjustment has to be carried out, special tools are required for removing the inner body and for fitting it again into the assembly. Such operations cannot be properly performed by unskilled persons using sewing machines in their homes, since the accurate adjustment of the shuttle is too difficult and requires skill. Therefore, rotary hook loop formers are not used for household sewing machines, and oscillating shuttles are preferred for this purpose, although they have disadvantages as compared with rotary loop formers. 5

It is one object of the invention to overcome the disadvantages of oscillating shuttles, and to provide a rotary looping device of simple construction which can be easily adjusted and used, and operated at high speed.

It is another object of the invention to couple a rotary hook by which a loop is formed, with drive means in such a manner that the formed loop can slip "between the drive means and the rotary hook and withdrawn by the needle.

Another object of the invention is to provide a rotary looping device for a sewing machine which produces little noise during operation.

Another object of the invention is to provide a household sewing machine with a rotary hook looping device.

Another object of the invention is to provide a rotary hook loop forming device with recesses and camming surfaces which facilitate the formation of loops of the desired shape.

3,396,688 Patented Aug. 13, 1968 Another object of the invention is to provide a rotary hook looping device which forms precise and well-formed stitches.

' Another object of the invention is to provide a rotary hook looping device for double needle sewing machines in which thread breakage due to untwisting of a portion of the tightened upper thread is avoided.

Another object of the invention is to prevent the rotary hook from catching the upper thread a second time during a second revolution of the rotary hook during which second revolution the stitch is to be formed without interference by the rotary hook.

With these objects in view, the present invention relates to an improved rotary looping device for a sewing machine. One embodiment of the invention comprises hook means mounted in a shuttle race for rotation in one direction about a first axis, and having a hook for catching a thread supplied by a needle, and for drawing a thread loop from the needle about the hook means during a revolution of the same; and rotary drive means having a second axis of rotation parallel to the axis of rotation of the hook means, and being preferably located in a common horizontal plane with the same.

The hook means has first and second diametrically disposed coupling cutouts located in a plane angularly spaced from the hook leading the same in the direction of rotation. The first cutout has such a shape and position that a portion of the thread loop formed about the hook means drops tensioned in the first cutout when passing the same during a revolution of the hook means.

The rotary drive means include first and second diametrically disposed drive members respectively located in the first and second coupling cutouts. Due to the eccentricity of the first and second axes, the drive members move alternately during a revolution of the drive means between a driving position engaging the respective coupling cutout and a disengaged position forming a gap with the respective cutout.

The tensioned thread loop portion is located in the first cutout spaced from the first drive member in the disengaged position of the same so as to pass through the gap between the first drive member and the respective first coupling cutout. During the continued revolution of the hook means, the thread is withdrawn by the needle through the gap between the second drive member and the second coupling cutout while the first drive member is in the driving position.

Due to the fact that the drive members alternately engage the respective coupling cutouts, the respective other drive member forms a gap with the respective coupling cutout, permitting successive slipping of the loop formed by the hook through the gaps formed between the disengaged drive member and the respective coupling cutout.

The timing of the reciprocating motion of the needle supplying the upper thread is selected in relation to the rotation of the drive means so that the upper thread is supplied at the proper moment, and the thread loop withdrawn at the proper moment determined by the position of the drive members.

The coupling cutouts are provided in angular or curved wall portions of the rotary hook means so that the tensioned loop portions extend along a chord spaced from the drive member in the driving position. The driving members project into the coupling cutout preferably a distance between 1.5 and 2 mm. In accordance with the present invention, it is not necessary to completely withdraw the drive member from its coupling cutout during the passage of the thread since the edge of the cutout is formed so as to coincide with a line connecting the caught portion of the thread loop with the needle in its lower position when the coupling cutout passes the needle.

In this manner, the present invention assures smooth drawing out of the thread even at high rotary speeds, which is not practical if the drive portion has to be completely withdrawn from the corresponding cutout. Therefore, the rotary hook means of the present invention is designed so that the thread drops into the coupling cutout during the formation of the thread loop by the hook, and while the respective drive member is located in the coupling cutout. Although cooperation between the drive member and the rotary hook means is maintained, the thread can be smoothly drawn out and easily passes the drive member.

While the upper thread loop is tensioned by the hook while being increased in size, the upper thread always assumes a correct position, the proper tension of the thread in the coupling cutout is maintained, and the thread is drawn out smoothly so that a perfect stitch is formed.

In accordance with the present invention, the drive means rotates at a constant angular speed, but the rotary hook means is driven to rotate at a varying speed. The speed variation of the rotary hook means depends on the eccentricity or distance between the axis of the drive means and the axis of the rotary hook means. The gap between the coupling cutouts and the drive member is provided in accordance with the invention only for the purpose of dropping the thread, and as the thread is dropped into the cutout while it is tensioned, the thread can be dropped into a very narrow gap of between 0.5 and 1 -mm., or even 0.4 mm. in the event that No. 20 sewing thread is used. Even very small gaps permit the abovementioned difference in the speed of rotation between the drive means and the rotary hook means. The construction is extremely simple, far simpler than the rotary shuttles of conventional industrial sewing machines. The rotary looping device according to the present invention has a construction very similar to the construction of an oscillating shuttle of the type used in household sewing machines, but nevertheless permits operation at high rotary speeds.

The rotary looping device according to the present invention produces very little noise during operation since it rotates making use of inertia and eliminating the noise created by stopping an oscillating shuttle. Only a very small gap between a driving member and a coupling cutout is required for permitting passage of the thread between the edge of the coupling cutout and one side of the drive member, and a gap of 1 mm. may be considered the maximum. The gap forms if the axes of rotations are eccentric, and in the most cases gaps of sufficient width are obtained if the eccentricity of the axes is ab out 0.5 mm. Since the eccentricity is so small, the rotary hook rotates almost as smoothly as if it were rotated by a coaxial drive means. In other words, very small impact forces will be developed by the drive member closing the gap and abutting the edge of the coupling cutout, and only very small movements in radial direction of the drive members in the cutouts take place due to the small eccentricity of the axes of rotation of the drive means and rotary hook means.

The rotary hook means according to the present invention is provided with a substantially semi-circular slot for the passage of the sewing needle so that the hook means can rotate substantially half a revolution while the needle is in the lower position located in the slot for placing the upper thread in the region of the bobbin.

In accordance with one embodiment of the invention, a recess is formed in an edge bounding the slot and permits formation of a well shaped loop just before the catching of the loop by the hook.

Depending on whether the lowered needle is located on the right side of the lower thread or on the left side of the lower thread, perfect stitches or unsuitable s'o-called hitch stitches are formed. Consequently, it is necessary that the needle rnoves downward on the right side of the lower thread, which is drawn out and somewhat loosened. Depending on its looseness, the thread is guided in the direction of rotation of the shuttle and is located at the right side of the region in which the needle moves, and consequently the needle is located at the left side of the lower thread so that hitch stitches may be formed.

In accordance with an embodiment of the invention, the rotary hook means is provided with a cam surface on its front wall by which the lower thread is guided and prevented from assuming a position on the right side of the moving needle, even if the drawn out and loosened lower thread is guided in the direction of the rotation of the rotary hook, whereby formation of undesirable hitch stitches is prevented.

When double needle stitching is used, the upper thread entangles with the lower thread, and a portion of the upper thread is untwisted while being tightened. In accordance with the present invention, the cam shape of the front wall edge of the rotary hook reduces the untwisting of the upper thread even if the lower thread is slackened, and thread breaks due to this cause are prevented.

Rotary loop forming devices of the type with which the present invention is concerned are constructed in such a manner that the rotary hook means performs two revolutions for a downward and upward reciprocating motion of the needle. The upper thread is caught by the hook during the first revolution whereupon the lower thread is pulled up. While the upper thread and lower thread form a seam and are tightened, the rotary hook performs asecond revolution and catches the next following thread loop during the third revolution. However, if too much of the upper thread is supplied due to low tension of the upper thread, or incorrect handling by the operator, it happens that the hook catches the upper thread again during the second revolution of the shuttle before the loop of thread formed by the rotary hook means is pulled up so that an irregular stitch is formed. The construction of the present invention prevents such occurrence.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary front view, partially in section, illustrating a sewing machine provided with a rotary looping device according to the invention;

FIG. 2 is a fragmentary end view of the sewing machine, partially shown in vertical section;

FIG. 3 is a front view of the rotary looping device;

FIG. 4 is a vertical axial sectional view of the device of FIG. 3;

FIG. 5 is an exploded perspective front view of the looping device;

FIG. 5a is a perspective rear view of the hook means of the looping device;

FIG. 6 is a series of fragmentary front views A to H illustrating a sequence of operational positions of the hook means during one revolution for forming a thread loop, and including two vertical axial sectional views D, H respectively correlated with front views D and H;

FIG. 7 is a front view on an enlarged scale illustrating the drive member of the device;

FIG. 8 is a side view, partially in vertical section, illustrating the drive member of FIG. 7;

FIG. 9 is a diagram showing in the form of graphs, rotary speeds of the hook means depending on the eccentricity of its axis in relation to the axis of the drive means;

FIG. 9a is a schematic diagram illustrating the relative positions of the drive means and rotary hook means;

FIG. 10A is a front view of the rotary hook means according to the preferred embodiment of the invention;

FIG. 10B is a view taken in the direction of the arrow B in FIG. 10A;

FIG. C is a side view taken in the direction of the arrow C in FIG. 10A;

FIG. 10D is a view taken in the direction of the arrow D in FIG. 10B;

FIG. 10B is a sectional view taken along line EE in FIG. 10B;

FIG. 10F is a view taken in the direction of the arrow F in FIGS. 10A and 10D;

FIG. 106 is a developed view illustrating the shape of a cam edge in the embodiment of FIG. 10A to FIG. 10F;

FIG. 11 is a plan view on an enlarged scale illustrating a rotary hook means according to the invention;

FIG. 12 is a series of elevational views a, b, c, d illustrating successive operational positions of a needle cooperating with the rotary hook means of FIG. 11;

FIG. 13 is a side view of the rotary hook means according to a modified embodiment of the invention;

FIG. 14 is a developed view illustrating the shape of a cam edge in the embodiment of FIG. 13;

FIG. 15 is a series of schematic front views A, B, C illustrating successive operational conditions during the formation of loops in a double needle sewing machine provided with a rotary hook means according to the invention;

FIG. 16 is a front view illustrating another embodiment of a hook means according to the invention; and

FIG. 17 is a plan view of the embodiment of FIG. 16.

Referring now to the drawings, and more particularly to FIGS. 1 to 5, a sewing machine 7 has an oscillating thread guiding arm 77 and thread tensioning means 76. A needle bar assembly 71 reciprocates a needle 5 through a slot in a presser foot 74 so that a fabric on top of the throat plate on the supporting bed or table 6 of the sewing machine is pierced by needle 5. Needle 5 is clamped by a screw 73 to the needle bar 71, and presser foot 74 is clamped to presser bar 72 by a screw 75.

A drive shaft, not shown, rotates a large bevel gear 78 which meshes with a bevel pinion 66 secured by a screw 67 to a drive shaft 3a which is mounted in hearings in the walls 62, 62' of the supporting table 6. A hearing sleeve 24 is provided in wall 62 and abuts a drive part 3. Another sleeve 64 is secured to drive shaft 32 by a set screw 65 so that axial displacement of sleeve 24 and drive part 3 is prevented.

As best seen in FIGS. 4, 7 and 8, drive part 3 has a hub 39 by which it is mounted on a portion of shaft 32, and two diametrically arranged drive members 33 and 34 projecting from a plate 31. Drive member 33 has a narrow rectangular outline as best seen in FIG. 7, and a slanted face 33 inclined to the axis and to the radial direction of drive part 3. Drive member 34 has a trapezoid outline with an edge 36 coinciding with the corresponding edge of plate 31, and another edge 38. A recess 37 is formed in plate 31 and drive member 34, and the extremity of drive member 34 is cut off at 38 to provide better guidance for a thread, as will be explained hereinafter. Drive part 3 is advantageously made of a synthetic plastic material.

As best seen in FIGS. 5 and 5a, the looping device includes a race 2, a rotary hook means 1, and a retainer cap 4 which is detachably secured to race means 2 by arms 26 to mount rotary hook 1 for rotation about the axis 0-0 which is parallel to and spaced a small distance from the axis O'--O' of the rotary drive means 3, 32. In the assembled condition of the looping device shown in FIGS. 3 and 4, drive members 33 and 34 are respectively located in coupling cutouts 15' and 15 in the rear wall 14 of rotary hook means 1. Rear wall 14 includes a substantially fiat circular center portion and a substantially irusto-conical or slightly curved annular slanted portion 14' so that the radially extending edges of cutouts 15 and 15 are angular. Due to the fact that drive members 33 and 34 are respectively located in coupling cutouts 15' and 15, the drive means 3, 32 is coupled with the rotary hook means 1 for rotation, but since the axes OO and O'O are spaced a distance e, relative movement between rotary hook means 1 and drive means 3, 32 takes place.

The coupling cutout 15 has a rectangular outline corresponding to the rectangular outline of the correlated drive member 33, but be somewhat larger than the same, as best seen in FIG. 6. The coupling cutout 15 is of trapezoidal shape, substantially corresponding to the shape of drive member 34, but being larger than the same, as best seen in FIG. 6. The slanted edge 10 of coupling cutout 15 is inclined the same angle as the corresponding lateral surface .36 of drive member 34, so that edges 10, 36 are parallel to each other and form a gap of uniform thickness in the position of FIG. 6D, and abut each other along the length thereof in the position of FIG. 6A.

As will be explained hereinafter in greater detail, the inclination of edges 10 and 36 is selected so that when a loop is formed by hook 16 of rotary hook means 1, a tensioned loop portion extends in the direction of the gap formed between the slanted edges 10, 36, as shown in FIG. 6D. The tensioned loop portion abuts edges 10' and 10" of coupling cutout 15, as best seen in FIG. 6D. Consequently, the tensioned loop portion of the thread is located along a chord inwardly of the extremity of drive member 34 and can pass under the same in the position of FIG. 6D.

The front wall 13a of rotary hook means 1 is annular and has a large central opening. Annular wall 13a is of substantially frusto-conical or curved shape and has an annular edge 13 which is shaped as a cam in the region 13'. The shape of cam edge 13 is best seen in FIGS. 10C and 10G.

A substantially semi-circular slot 18 is provided in rotary hook means 1 for the reciprocating needle 5. In accordance with the invention, a wall of slot 18 has a recess 18', best seen in FIGS. 5, 5a, 11 and 12. The angular position of slot 18 in relation to hook 16 is selected so that the needle can reciprocate through slot 18. A bobbin supporting pin 19 projects from the center portion of rear wall 14 so that a bobbin inserted through the central opening of front wall 13a can be attached to pin 19 within the rotary hook means 1, and also removed from the same without difficulty. In the diagram of FIG. 106 it is assumed that the hook 16 is located in the position P. The edge 13 of wall 13a extends first in a plane perpendicular to the axis of rotation an angle of The cam edge 13 gradually rises from point Q to point R between the angular positions 85 and and is then again located in a plane perpendicular to the axis of rotation. At the point T corresponding to an angle of 310, the cam edge 13 drops again to the point P. The rise of the cam edge may be between 1 and 2 mm. The raised cam dwell presses the lower thread during rotation of the rotary hook member so that a loosening of the lower thread is prevented, and it is assured that the needle always moves down on the right side of the lower thread to prevent the formation of hitch stitches. The construction of the rotary looping device of the invention permits the drawing out of the lower thread at a high speed so that the tendency of the lower thread to flex is increased, but flexing of the lower thread is prevented by the cam edge 13 so that the needle moves downward on the right side of the lower thread to assure the formation of a correct stitch.

As best seen in FIGS. 11 and 12, the recess 18' in the connecting portion 11 between hook 16 and the blunt end of the circular slide surface 12, aids in forming a loop of the upper thread N.

When the needle enters the slot 18, a loop is freely formed due to the rising motion of the needle in the region of recess 18'. The formed thread loop is pushed into recess 18, and the loop is reliably formed forwardly of the hook 16 in the direction of rotation and is guided until caught by hook 16. It will be seen that the point of hook 16 moves during rotation of rotary hook means 7 1 into the region in which a loop of thread N is permited to expand in the region of recess 18'.

In the position of FIG. 12a, the needle 5 moves downward and the thread N is drawn out in a position closely adjacent the needle and between the edges of a narrow portion of slot 18. In the position of FIG. 12b, the needle has started its upward stroke, so that a loop begins to form in the usual Well-known manner. The positions of the needle in relation to the rotary hook means 1 corresponding to FIGS. 12a, 12b, 12c and 12d are shown in FIG. 11 by lines a-a', b-b', c-c, and d-d. It will be seen that in the position of the needle shown in FIG. 12b, the rotary hook means has turned to a position in which recess 18' is located opposite the needle, so that sufficient space for the formation of a loop is available. Since the opposite edge of slot 18 is not recessed, it pushes the thread loop into the recess 18' during the upward movement of the needle. In the position of FIG. 120 when the lower end of the thread loop is already located outside of the slot, a narrowing portion of recess 18 is located opposite the needle, and in the position of FIG. 12d, the retracted needle is located in the unrecessed portion of slot 18. Directly thereafter, the rotary hook means turns to a position in which hook 16 engages the thread loop.

The rotary hook means 1 has a circular guide surface 12 which slidingly engages the circular surface 22' of race means 2. An annular shoulder 22" abuts one lateral surface 12a of hook means 1 so that surfaces 22 and 22" form a bearing 22 for rotary hook means 1. A retainer cap 4 is fitted into the annular surface 21' of race 2 and has an annular surface 47 abutting an annular shoulder of race 2, and also the annular front surface 12b of hook means 1 so that hook means 1 is retained in the race and supported in the same for rotation about the axis O-O.

A pair of locking arms 26 is mounted on race 2 turnable about pivot means 27. When the arms 26 are turned inwardly, they engage pins 45 on the wall 41 of the retainer cap 4 and hold the retainer cap firmly on race 2 in the assembled position shown in FIG. 4. Arms 26 are preferably resiliently mounted.

A notch 29 is provided in the outer wall of race 2. and engages a guide pin 29a, see FIG. 4, to angularly position retainer cap 4 on race 2. The top of retainer cap 4 is flattened, and a spring 42 is secured to the same by screws 44. Spring plate 42 has a rectangular cutout 43 for the passage of the needle 5 into the race 2 which is cut off on top to permit entry of the needle through cutout 43 and slot 18 into the interior of hook means 1. A cutout 46 in wall 41 engages a corresponding projection on the bobbin case, not shown, to hold the same in a correct angular position.

Drive shaft 32 passes through the bushing or sleeve 24 which is secured by arms 23 to a Wall 23' of race 2.

As noted above, the drive members 33 and 34 are located in coupling cutouts 15' and 15 of corresponding shape in the assembled condition of the device shown in FIG. 4. The extremity of drive member 33 is flattened at 33 as best seen in FIGS. 8 and 5. The axial extension of drive members 33 and 34 is substantially the same, and the position of bushing 64 is selected so that drive members 3-3, 34 project in the corresponding coupling cutouts a selected distance which may be 2 mm. It will be noted that the radial extension of the rectangular drive member 33 is greater than the radial extension of the trapezoid drive member 34, while drive member 34 is wider than drive member 33.

In accordance with the present invention, drive members 33 and 34 have different functions in controlling the thread. The slant of drive member 34 permits the upper thread to pass in straight tensioned condition along the correspondingly slanted edge 36 to a position forming a :cord between the outer and inner edges 10" of coupling cutout 15, as best seen in FIGS. 6D and 6D. This position is assumed, for example, when the rotary hook means 1 has turned an angle between and from the lowest position of the needle. It must then be prevented that the drive member 34 catches the upper thread during the rotation of book means 1, and the respective portion of the upper thread on rear wall 14 is moved toward the center of hook means 1 and taken from drive member 34.

Hook 16 rotates over an angle of 200 while drive member 33 reaches the region of the needle, so that the thread is drawn off drive member 33 by the upward motion of the needle. The purpose of drive member 33 is to hold the upper thread so that the same is not caught when the thread is drawn out on the sides of the center of rotation 0 of drive part 31. Accordingly, drive member 34 is formed with a gently curved surface so that the thread is suitably bent and guided over the center part of drive part 31, and can be drawn out in upward direction.

Referring now to FIG. 6 it Will be seen that the axis OO of the drive means 3, 32 and the axis O'O' of hook means 1 are located spaced a distance e in a common horizontal plane. A cover or throat plate 61 is shown in FIG. 6 to have an opening through which the needle passes with the upper thread N. In the position of FIG. 6A, the slanted edge 36 of drive member 34 is in full contact with the slanted edge 10 of the coupling cutout 15, and while drive member 34 turns about axis 0, hook means 1 is turned by drive member 34 about the axis 0. In the posiiion of FIG. 6A, hook 16 is located under the needle opening in plate 61 and has just caught the thread N. In FIG. 9, which will be explained in detail hereinafter, hook means 1 would be in this position after having turned an angle of 315.

Hook means 1 is successively turned by drive member 34 to the positions of FIGS. 6B and 6C while the size of the thread loop is gradually increased, portions of the thread loop sliding on the rear and front walls of rotary hook 1. Due to the eccentricity of the axes OO and OO', drive member 33 moves to a driving position engaging a corresponding edge of coupling cutout 15' in the position of FIG. 6D, while the slanted edge of drive member 34 moves away from the slanted edge 10 of coupling cutout 15 to form a slanted gap. The inclination of edges 10 and 36 is soselected that the slanted gap extends in the direction in which the thread loop is oriented due to the position of hook 16. The tension of the thread loop causes the thread portion sliding on rear wall 14 of hook means 1 to enter into the gap between the slanted edges 36 and 10 until the tensioned thread portion forms a cord between edges 10' and 10 of coupling cutout 15, as best seen in FIG. 10D. In this position, the portion of the thread in cutout 15 is located inwardly of the extremity of drive member 34 so that during further rotation of drive member 34 and hook means 1, the thread portion slips under the extremity of drive member 34 and assumes first the position shown in FIG. 6B, and then passes out of cutout 15 to move to the position of FIG. 6F. The size of the loop is greatest in the position of FIG. 6E. In the position of FIG. 6F, the thread approaches the innermost portion of drive member 33 which does not project into cutout 15 as best seen in FIG. 4. When the drive means and hook means have turned to the position of FIG. 6G, drive member 33 does not engage the edge of the corresponding coupling cutout 15 and the thread slides in curved condition over the extremity 33' of drive member 33 whereupon it is drawn out by the operation of the needle. After further rotation, the position of FIGS. 6H and 6H is assumed in which the thread on the rear wall of hook means 1 can easily pass through the gap between drive member 33 and the outer edge of cutout 15'. During the following revolution of hook means 1, the upper thread is sufficiently tightened to complete a stitch with the lower thread, not shown, while during the third revolution, the operations shown in FIG. 6 are repeated.

Referring now to FIG. 9a, drive part 3 rotates at constant angular speed about the axis while hook means 1 rotates about the axis 0 which is spaced the distance e from the axis 0'. A vertical plane G-G passes through axis 0, and a vertical plane GG' passes through axis 0'. Plane GG' intersects with the circle representing the extremities of drive members 33, 34 in two points I and H; an angle 1, O, H is thus formed. It will be seen that during rotation of drive means 3, 33, 34 through an angle of 180 located on the left side of plane GG, hook means 1 will not turn through 180, but only the angle 1, O, H, whereas during turning of the drive means over 180 on the right side of plane GG, hook means 1 will turn over an angle greater than 180 which is the difference between 360 and angle I, O, H. Consequently, the rotary speed of hook means 1 varies during each revolution. The rotary speed is smaller when the respective driving member is located on the side of axis 0', and is greater when the drive member is located on the side of axis 0. FIG. 9 illustrates the speed ratio k between the drive means 3 and the hook means 1 for different distances 2 between axes O and O, the distances e being indicated for half millimeters between 0 and 3 mm. In FIG. 9 it is assumed that the radial distances of the drive members 33, 34 from the axis 0 of the drive shaft are equal, while actually the radial distances of drive members 33, 34 are different in the preferred embodiment of the invention so that the illustrated speed graphs are not quite accurate. The graphs in FIG. 9 show the rotary speeds of hook means 1 for different eccentricities e. The varying speed of book means 1 over the angle from 0 to 360 is shown. The origin 0 is assumed to be at the point where the rotary speed of hook means 1 is a maximum which is the case when drive member 33 is located in the horizontal plane defined by axes O and O, and drive member 33 is located in this horizontal plane at the right side of axis 0' of the drive means.

For example, the rotary speed of hook means 1 is continuously changed between the ratio 0.83 and 1.28 assuming an eccentricity e of 3 mm., and assuming an eccentricity of 2 mm. the ratio between the speed of the drive means and the speed of the hook means is between 0.87 and 1.17.

In a preferred embodiment of the invention in which the eccentricity e is 0.5 rnm., the speed ratio is between 0.95 and 1.035.

Hook means 1 is turned by drive member 34 between the angle 210 and the angle of 20 20' passing through the 360 position. The 315 position is illustrated in FIG. 6A, while the angle of 20 20' is passed between the positions of FIGS. 6C and 6D.

At the angle of 20 20' drive member 33 engages the edge of the coupling cut out and drive hook means 1 until the angle of 210 is reached. Consequently, while each of the drive members 33 or 34 is in the driving position, the speed of hook means 1 varies. Since drive members 33 and 34 are diametrically disposed, the speed of hook means 1 is momentarily increased in the angular positions 20 and 210. After hook means 1 is rotated by one drive member first at a high speed and then at a lower speed, the other drive member takes over so that the speed of the hook means is changed from a low speed peak to a high speed peak. The angle of 135 in FIG. 9 corresponds to the position of FIG. 6E, the angle of 180 corresponds to the position of FIG. 6F, the angle of 225 in FIG. 9 corresponds to FIG. 66, and the angular position 270 corresponds to the position of FIG. 6H and FIG. 6H.

At the moment of change-over from one drive member to the other drive member, and assuming an eccentricity e of 3 mm., hook means 1 rotates at a speed which is in the ratio 0.835 in relation to the rotary speed of the drive means, and is momentarily accelerated to the higher speed which is in a ratio of 1.235 to the rotary speed of the drive means.

Assuming that the average rotary speed of book means 1 is 2,000 r.p.m., hook means 1 rotating at a speed of 1670 r.p.m. while driven by one of the drive means, it is accclerated to a speed of 2470 r.p.m. when the other drive member becomes operative and assumes the driving position. Such an acceleration may cause a noisy impact of the second drive member on the rotary hook means. However, in accordance with the present invention it is sufficient to select an eccentricity of only 0.5, as indicated by a broken line in FIG. 9 so that the speed difference at the moment of changing over from one drive member to the other drive member is very small and only about 0.070 of the ratio between the rotary speed of the drive means and the rotary speed of the hook means, so that the impact and shock is reduced to be negligible. In the illustrated embodrnient, the axes O and O are located in a. horziontal plane, but axis 0 may be located within the range of 20 above or below the horizontal plane to axis 0.

FIGS. 13 to 15 illustrate a modified embodiment of the hook means in which the cam edge of front wall 13a has a different shape. This embodiment is suitable for sewing machines with twin needles. The shape of cam edge 13" corresponds to the shape of cam edge 13 in the regions Q to T as is apparent from a comparison of FIGS. 106 and 14. However, at a point P' the cam edge drops in the angle between 20 and 40 to permit the thread loop to release the lower thread N and to reduce its tension so as to prevent a break of the upper thread. This will be best understood with reference to FIG. 15. When twin needles are used, thread breaks occur particularly in the upper thread on the left when a straight seam is made of small stitches and at a small feeding speed of the' fabric. The thread breakage is caused when the left seam is made of hitch stitches which cause untwisting of the left upper thread N When the upper threads N N move off the rotary hook 1 as shown in FIG. 15A, the left upper thread N is turned to the position shown in FIG. 15B and then moves to its uppermost position through the position shown in FIG. 15C. During the movement of thread N from the position of FIG. 15B to the position of FIG. 150, the lower thread N has an influence on the untwisting of the left upper thread N When the left upper thread N is tightened and tensioned, it is pulled up while entangled with the lower thread N as shown in FIG. 15C, and thread N rubs thread N and untwists the same. At the same time, filaments and fibers of the thread N are frayed. When some filaments of the frayed and damaged thread are caught by the rotary hook, thread breakage occurs. However, in the construction of the present invention, the drop of the cam edge in the region P, P" reduces the untwisting of the upper thread N and prevents the breaking of the thread.

FIGS. 16 and 17 illustrate another embodiment of the hook means according to the invention which is modified to prevent the catching of a thread loop during every second revolution in which the stitch is tightened, and no thread is to be caught. In the portion 11 where the recess 18 is provided, a projecting tongue 20 is formed at the blunt end of the portion 12 spaced a distance )3 from one side of the slide surface 12, and a distance a from the outer periphery of the same. The projecting tongue 20 is formed so as to be out of the way of the thread loop which is pushed out into the recess 18', as explained with reference to FIGS. 11 and 12. The projecting tongue 20 pushes the thread loop to one side thereof toward the rear wall 14 so that catching of the thread by the hook 16 is not possible. Due to this construction, the mechanism can be operated at very high speed without the danger of catching the thread in an undesired manner before a stitch is tightened.

Referring again to the operation of the looping device of the invention, the tensioned loop in the position of FIG. 6D fits into the narrow gap between edges 10 and 36 which extend in the same direction so that the tension of the thread draws the thread into the cutout 15 to a position abutting the edges and 10" permitting passage of drive member 34. Due to this arrangement, a very small gap is required between the drive member 34 and the coupling cutout 15, and consequently the eccentricity of the axes O and O can be selected to be very small, so that a drive means and the rotary hook means rotate at almost the same speed, and noisy impacts of the drive members on the corresponding edges of the coupling cutouts and 15' are avoided. Since the tensioned thread portion drops into the proper position in cutout 15 due to its tension, the passage of the thread is very smooth, and the same is true -for the passage of the thread through the gap between drive member 33 and cutout 15 which takes place under the pulling force of the retracted needle. Due to the easy passage of the thread between the drive members and the coupling cutout, the rotary looping device of the invention can operate at high speed, while nevertheless the drive members are at all times located in the coupling cutouts, and do not have to be retracted from the same for the passage of the thread. As a result, the rotary looping device of the invention operates with very little noise, and causes practically no abrasion of the thread although operated at high speed.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of loop forming de vices for sewing machines differing from the types described above.

While the invention has been illustrated and described as embodied in a rotary hook means having a coupling cutout cooperating with a driving member rotating about an eccentric axis and forming a gap for a tensioned thread with the drive member, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations s'hould and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A rotary looping device for a sewing machine, comprising, in combination, race means having a first axis; needle means for moving a thread into said race means and out of the same; book means mounted in said race means for rotation in one direction about said first axis, and having a hook for catching said thread and for drawing the same from said needle means to forma thread loop about said hook means during a revolution of the same, said hook means having a rear wall normal to said first axis and an angular wall portion extending from said rear wall toward a plane generated by said hook rotating in said race means and having first and second coupling cutouts located angularly spaced from said hook, said first cutout positioned in said rear wall and extends into said angular wall portion so that a tensioned portion of said thread loop formed about said hook means drops into said first cutout when passing the same during a revolution of said hook means; and rotary drive means having a second axis of rotation parallel to said first axis and including first and second drive members respectively located in said first and second coupling cutouts and alternately moving during a revolution of said drive means between a driving position engaging the respective coupling cutout and a disengaged position forming a gap with the respective cutout, said tensioned loop portion dropping through said gap into said first cutout to a position located inwardly of said first drive member so as to pass the same during rotation whereupon said 12 thread loop is withdrawn by said thread take-up lever through the gap between said second drive member and said second coupling cutout wfhile said first drive member is in said driving position.

2. A rotary looping device according to claim 1 wherein said first and second axes are located in a common plane, said common plane being located within the range of 20 above and 20 below a horizontal plane.

3. A rotary looping device according to claim 1 wherein the distance between said first and second axes is approximately 0.5 mm.

4. A rotary looping device according to claim 1 wherein said device member has a slanted edge; wherein said first coupling cutout has a slanted edge located opposite said slanted edge of said first drive member and extending parallel to the same so that said slanted edges fully abut in said driving position, and form a gap in said disengaged position of said first drive member, the direction of said slanted edges being such that when said gap is formed due to the eccentricity of said first and second axes, said hook holds said thread loop in a position extending in the same direction as said slanted edges in said gap so as to be drawn by the tension thereof through said gap and into said first coupling cutout.

5. A rotary looping device according to claim 4 wherein said first coupling cutout is formed in said angular wall portion of said hook means so that said slanted edge of said first cutout is angular and has a projecting center portion engaged by said first drive member, and two end portions forming radially outer and radially inner edges on which the tensioned thread abuts to form a chord spaced from said first drive member while the same is located in the region of said center portion of said angular edge in said disengaged position.

6. A rotary looping device according to claim 1 wherein said first drive member has a trapezoidal outline in a plane perpendicular to said axes; wherein said first coupling cutout has a trapezoidal outline in said plane having an area greater than said rectanglar outline of said first drive member; wherein said second drive member has a rectangular outline in said plane; and wherein said second cutout has a rectangular outline in said plane having an area greater than said rectangular outline of said second drive member.

7. A rotary looping device according to claim 6 wherein radially inner end of said first drive member is spaced a greater distance from said second axis than a radially inner end of said second drive member.

8. A looping device according to claim 7 wherein said second drive member has a surface gradually rising to an extremity from the radially inner end to the radially outer end thereof for guiding a thread pulled up by said needle means out of said second coupling cutout.

9. A rotary looping device according to claim 1 wherein said drive means include a drive part having said first and second drive members, said drive part being made of a synthetic plastic material.

10. A rotary looping device according to claim 1 wherein said hook means has a rear wall formed with said coupling cutouts, a central annular part having said hook, and a front wall forming a substantially semicircular slot with said central part, said central part being formed with a recess adjacent said hook and opening into said slot to increase the width of the same so that said needle means while moving upward in said slot forms a thread loop projecting into and being guided by said recess.

11. A rotary looping device for a sewing machine as claimed in claim 1 wherein said rotary hook means has a rear wall formed with said coupling cutouts, and an annular front wall having an edge bounding a central opening for the insertion of a bobbin case; and wherein a part of said annular edge is formed as a cam edge for displacing the thread sup-plied by said needle means.

12. A rotary looping device according to claim 11 13 wherein said cam edge has within an angular region of 20 a dropping cam edge for guiding the thread to prevent fraying of the upper thread and thread break.

13. A rotary looping device according to claim 1 wherein said rotary hook means has a rear wall formed with said first and second coupling cutouts, an annular front wall, and a central portion between said front wall and rear wall and having said hook and a blunt end spaced from said hook, and including a circumferentially projecting tongue projecting from said blunt end toward said hook spaced from the same, from said rear wall, and from the periphery of said central portion and adapted to guide the thread of said needle means to prevent catching of the thread by said hook when said needle means forms a stitch during a revolution of said hook means.

14. A rotary looping device according to claim 1 wherein said first and second axes are substantially located in a horizontal plane; wherein said first drive member and said first coupling cutout have parallel edges forming a gap when said hook forms a thread loop extending from said needle means to said book along said edges so that tensioned portion of said thread loop enters into said gap.

15. A rotary looping device according to claim 14 wherein said edges and said gap extend in the direction of said tensioned portion of said thread loop when said first drive member and said first coupling cutout form said gap during rotation of said hook means.

References Cited UNITED STATES PATENTS 480,182 8/1892 Dial 1l2228 607,080 7/ 1898 Richards 112-189 1,299,468 4/ 1919 Hohmann 112--228 1,343,823 6/1920 Hohmann 112189 2,148,385 2/ 1939 Waterman 112228 2,941,488 6/1960 Attwood 112-228 3,074,367 1/1963 Habedank et al 112228 3,155,061 11/1964 Goebel et al 112181 2,219,470 10/ 1940 Carlson 112-232 HERBERT F. ROSS, Primary Examiner.

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