US3443540A - Thread trimming device for lockstitch sewing machine - Google Patents

Description

13, 1969 v F, HANNEMANN ET AL 3,443,540

'THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967 Sheet of 6 INVENTORS," Q

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THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967 Z of 6 Sheet INVENTORJ:

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THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967 Sheet 3 of 6' y 1969 F.IHANNEMANN ETAL 3,443,540

THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Fild Feb. 27, 19s?- Sheet 4 of s y 1939 r F. HANNEMANN ET AL 3,443,540

THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 15567 Sheet FIG.17

May 13, 1969 H MA ETAL 3, 143540 THREAD TRIMMING DEVICE FOR LOCKSTITCH SEWING MACHINE Filed Feb. 27, 1967 Sheet 6 of s United States Patent In. or. Dosb 65/02 US. Cl. 112-252 14 Claims ABSTRACT OF THE DISCLOSURE A device for the simultaneous trimming of the needle thread and the bobbin thread underneath a workpiece after the completion of the seam, for use with lockstitch sewing machines. An arcuate blade oscillates concentrically about the looper, and cooperates with a stationary blade controlled by the driving and stop means of the sewing machine by means of cam discs, electromagnets or fluid motors. This device can be aldditionally installed in existing sewing machines without any special provision, and can also be used in lockstitch sewing machines provided with a narrow work-supporting arm and which are further provided in the usual manner with, or are without, an own feed dog device, to be used in automatic sewing systems, whereby either the :workpiece is directed past the sewing machine or the sewing machine is directed past the worpiece by means of a special feeding device.

Background 0 the invention This invention is in the field of US. patent classification class 112252, entitled, ElementsThread Cutting.

The object of the invention is to provide a thread trimming device, which assures rapid operation, a high degree of security and simple manipulability, whereat .after trimming the needle and bobbin threads underneath the workpiece, the residual thread ends have a short length.

It is a further object of the invention to provide a device which is simple in construction and relatively small in its dimensions.

A further object of the present invention is to enable the device to be additionally attached to existing machines without demounting essential driving members, for instance the looper shaft, and insertion of an additional operational mechanism into the machine.

It is also an object of the invention to create a thread trimming device which has a small number of mechanical parts. Finally, it is an object of this invention to dispense with an additional control device for loosening the needle thread tension, required before operation of the thread trimming device.

There are already known devices for trimming both the needle thread and the bobbin thread after finishing a seam underneath a workpiece. In such devices the needle and bobbin threads are trimmed simultaneously by a hooked thread-catch device having a cutting edge and cooperating with a fixed knife, whereby the thread-catch device and the fixed knife are arranged below the throat plate and parallel with it.

These thread trimming devices are essentially used with group stitch sewing machines, :which have a control disc for the guided control of the feed dog,-the stop mechanism and the thread trimming knives after engaging the sewing machine for perfonmance of a sewing cycle. Such an arrangement is disclosed in German Patent 417,- 429, issued on J an. 29, 1924.

A thread trimming device for lockstitch sewing machines provided with a thread-catch device attached to a slidable carrier and cooperating with a fixed knife, whereby the thread-catch device, when in an ineffective and rest position is movable into a releasable driving connection with the looper, is disclosed in German Patent 341,771 of Aug. 22, 1919.

There are also known thread trimming devices employing thread-catch devices consisting of a ring or segment which envelopes the looper casing, Whereat the ring is mounted on an oscillating carrier arranged coaxially with the looper, said carrier being in releasable driving connection with the loop taker shaft.

These devices are disclosed in German Patent No. 353,627 of Sept. 8, 1918 and US. Patent No. 3,173,392 to Hedegaand. To cut the threads, the sewing machine has to be stopped initially at the lowest position of the needle before a starting lever, which couples the actuating shaft of the thread-catch device with the looper-actuating shaft through a gear train, may be operated.

According to another proposal it is possible to operate said starting lever when the machine is still running. In this construction the starting impulses is accumulated until the armshaft of the sewing machine has reached the starting position, in which the thread-catch device can come into operation. Such an arrangement is disclosed in US. Patent No. 3,141,432 to Reeber et al.

These known devices require a relatively high amount of mechanical coupling and actuating members which, in spite of their location in the smallest place in an annexaggregate, increase the size of the machine. In addition, the later attachment of such an annex-aggregate to a sewing machine already at hand is difficult.

Summary According to the invention the objects are solved substantially by the provision of a rotating carrier for the trimming blade, whereby the carrier is in driving connection with a first cam disc driven directly or indirectly by the actuating means for the driving and stop means of the sewing machine.

Said first cam disc is operably connected with a second cam disc mounted on the rotary feed lifting shaft to influence the action of the first cam disc for the purpose of drawing off the threads and blocking the thread trimming device and the stitch forming elements.

The cam discs are in driving connection with each other by means of a rocker arm having rollers abutting against said cam discs. The rocker arm is pivoted in the bed plate of the sewing machine. The first cam disc which is in driving connection with the carrier for the arcuate blade is pivoted on an axle and is provided with a hollow for receiving a roller pivoted to the rocker arm, in order to keep it out of the effective range of the second cam disc during the operation of the machine. The second cam disc has a control surface for influencing the movement of this first cam disc. This first cam disc is also provided with a control surface for the purpose of preventing a jerky drawing off of the bo bbin thread from the bobbin through the arcuate blade, when performing a torsional moment to said first disc cam in interaction with both control surfaces.

The second disc cam is formed with a recess on its control surface for receiving the roller of the rocker arm. 0n the first cam disc there is provided a control surface section to impart an accelerated movement to the arcuate blade during the cutting action, in cooperation with the second cam disc.

For driving the first cam disc a rotary magnet, convided for the first cam disc, for leading it back into its normal position.

However it is also possible to use a lifting magnet or a fluid-motor which is in driving connection with the first cam disc and controlled by the stop mechanism of the sewing machine by means of a lever and a pin attached to the first cam disc.

Below the table plate there may be provided a lever for a direct driving of the first cam disc, which is provided with a pin and is in driving connection with the lever between it and afoot treadle of the driving motor, in such a manner that at a backward movement of said foot treadle the pressure induced by the foot acts elastically upon the first cam disc.

An actuating rod is pivoted on the foot treadle and is in effective connection with a known mechanism for lifting the presser foot and for releasing the needle thread tension in such a manner, that at a backward movement of the foot treadle, first the needle thread tension will be loosened and afterwards the presser foot will be raised. The arcuate blade, attached to the rotating carrier and cooperating with a stationary cutting blade, has a baflle attached to the bed plate for the purpose of assuring a positive application of the trailing age on the arculate blade during cutting off the threads.

Furthermore, the arcuate blade has a groove for the receiving of the threads during its withdrawal from the thread supply. The groove ends in a clearance and its trailing edge coacts with the stationary cutting blade. The oscillating carrier for the arcuate blade is cup-shaped and is pivoted in a ball bearing bracket. The bearing bracket houses a stuffing for the looper shaft.

In lockstitch sewing machines, provided with a narrow work supporting arm, which do not have their own feed dog, the cam discs and the rocker arm can be placed in the trailing part of the supporting arm, whereat the driving connection between the cam discs and the oscillating carrier can be effected through an intermediate shaft provided with gear wheels.

Brief description of the drawings FIG. 1 is an elevational view of a frame with a motor and a sewing machine, embodying the present invention.

FIG. 2 is a left view of a part of the sewing machine with the trimming device.

FIG. 3 is an enlarged part view of the arcuate blade, stationary cutting blade and bafile, partially in section.

FIG. 4 is a top plan view of the parts shown in FIG. 3.

FIG. 5 shows the parts of the thread trimming device on the sewing machine, in nonoperative position.

FIG. 6 shows the thread trimming device at the beginning or the trimming process.

FIG. 7 shows the thread trimming device with the arcuate blade in its thread-drawing off position.

FIG. 8 shows the device in the thread trimming position.

FIG. 9 is a vertical section taken on line 99 of FIG. 2 with the thread trimming device being operated through a lever by a lifting magnet, a fluid motor or a pedal.

FIG. 10 is a vertical part section taken on line 10--10 of FIG. 11.

FIG. 11 is a view of FIG. 10 in direction of the arrow A.

FIG. 12 is a view of the looper, the carrier for the arcuate blade and its driving means, with the device arranged in a sewing machine having a work supporting arm.

FIG. 13 is a top plan view of the work supporting arm of a lockstitch sewing machine partially in section.

FIG. 14 is a vertical section on line 1414 of FIG. 13.

FIG. 15 is a side elevation of a driving aggregate for the thread trimming device with a lifting magnet.

FIG. 16 is a side elevation of a driving aggregate including a compressed air motor.

FIG. 17 is a front elevation of a sewing machine, by which the operation of the trimming device, the needle thread tension, the presser foot, and the motor will be effected through a linkage by means of a edal.

FIG. 18 is a closed schematic view of the linkage and the pedal, seen in direction of the dart B of FIG. 17.

FIG. 19 is a side elevation of an operation device for the thread trimming device and a linkage for releasing the thread tension and for lifting the presser foot.

FIG. 20 is an enlarged detail of FIG. 19, in front elevation.

Description of the preferred embodiment Referring to FIGS. 1 and 17, there is shown a lockstitch sewing machine having a conventional bed plate 21 supporting an upright 22 carrying an overhanging arm 23 which terminates in the sewing head 24. Pivoted within the arm 23 is the main drive shaft 25, operably connected with a reciprocating needle bar 27 carrying the needle 26. Secured to the arm drive shaft 25 is a pulley 28 driving the loop taker shaft 30 with the looper shaft 32 cooperating with the needle 26 and secured to the shaft 30 over a transmission belt 29 and a second pully 31 mounted on the looper shaft 30. The looper 32 performs in known manner two revolutions during each complete oscillating cycle of the needle 26.

The front end of the looper shaft 30 (FIG. 9) is embraced by an oil retainer 33 mounted in a bearing bracket 34, which is fastened to the bed plate 21 by screws 36. A gasket 35 is interposed between the bed plate 21 and a flange 37 of the bearing bracket 34 having beveled raceways 38 for balls 39, which effects a frictionless pivoting of a cup-shaped carrier 40 for an arcuate blade 42 attached to it with screws 41.

The balls 39 are disposed in an annular groove 43 profiled in the carrier 40.

The carrier 40 is formed with a sliding surface 44 with a V-shaped gate for receiving balls 45. The outer support for the balls 45 is a ring-shaped flange 46, having on its tube-formed part 47 a winding 48 which is screwed in in the bearing bracket 34. The looper 32, fastened to the looper shaft 30 by a screw 49, has a recess 50 receiving the flange 46 and the carrier 40. On a section of its circumference the carrier 40 has a gearing 51 (FIG. 2) for the cooperation with a toothed sector 52 of a cam disc 53.

The cam disc 53, having a prolongation 54, is fitted in a bore 57 on the bed plate 21. The axle 56 is fitted in the bed plate 21 and fastened by a screw 58. Two spring rings 59 on both sides of the cam disc 53 prevent its axial movement on the axle 56. On its control face 59' the cam disc has a hollow '60 for receiving a roller 61, pivoted on one end of a rocker arm 62. The rocker arm 62 is supported for oscillation on an axle 63, fastened to the bed plate 21. The other arm of the rocker arm 62 carries a rotating roller 64, which can rest against the control face 65 of a cam disc 66, mounted on a rotating shaft, in this case on the feed dog lifting shaft 67.

A coil spring 68 effects the resting of the disc cam 53 with its hollow 60 against the roller 61 for the purpose of holding the rocker arm 62 and its roller 64 out of the sphere of activity of the cam disc 66 during the operation of the sewing machine.

Fastened to the carrier 40 is an arcuate blade 69 (FIGS. 2 to 8) having two points 70, 71, which are directed contrary to in the sense of rotation of the looper 32. The arcuate blade 69 is reduced in its thickness towards the points 70, 71. Between the points 70, 71 there is inserted a groove 72 for the needle thread 73 and the bobbin thread 89'. The groove 72 ends in a clearance 74, the trailing edge 75 of which cooperates with a cutting edge of a stationary cutting blade 77. The cutting blade 77 and a baffle 78 for the arcuate blade 69 are fastened by screws 80, 81 to a jib 79 arranged at the bed plate 21.

During a torsional counterclockwise movement, bearing upon the cam disc 53, the roller 64 of the rocker arm 62 will be pressed against the cam disc 66. This is effected, after stopping the machine when the needle 26 is in its low position, by a lifting magnet 82 through a lever 83 and a roller 84 pivoted to the disc cam 53. (See FIGS. 5, 9 and 15.)

The arcuate blade 69 will have moved to the needle 26 by several angular degrees. During the movement of the machine caused by rotating the hand wheel 85 (FIG. 1) or by a driving motor 86 which is provided with an automatic stop and rotary device moving the machine which has stopped in a low position of the needle into a position in which the needle 26 is at high position, the roller 64 gets to a control surface 87 of the cam disc 66. After this the roller 61 of the rocker arm 62 is disconnected from the hollow 60, so that in cooperation with a control surface 88 on the cam disc 53 the arcuate blade 69 with its point 70 may enter the thread triangle formed by the needle thread 73 and may engage the bobbin thread 89' and the needle thread 73 leading to the work piece.

The control surfaces 87 and 88 cooperate with each other over the rocker arm 62 and are shaped in such a manner, that when the bobbin thread 89' is seized by the arcuate blade 69, a jerky drawing off of this thread and consequently an overslipping of the bobbin in its case will be prevented.

The stationary blade 77 is mounted near the stitch-hole to get short thread ends beneath the work piece 90 after the threads have been trimmed. On the other hand, the needle thread 73 leading to the needle 26 may be cut off proportionally long, to avoid its withdrawal from the needle 26, when forming the first stitch after trimming.

Also the bobbin thread 89 has to be cut off long enough to get a satisfactory stitch formation at the start. During the drawing off of the thread, the needle thread 73 and the bobbin thread 89 FIG. 7, lie in the groove 72. Immediately before the roller 64 falls into the recess 91 (FIG. 8) of the cam disc 66 the threads 73, 89' will be trimmed as the trailing edge 75, contained in the clearance 74 of the arcuate blade '69, passes by, by the cutting edge 76 of the stationary cutting blade 77. After lifting the presser foot 92, the work piece 90 may be removed. Due to the falling of the roller 64 into the recess 91, the sewing machine is stopped until the cam disc 53 is shifted back into its normal position (FIG. 5) by means of the coil spring 68 and the releasing of the lever 83.

The cam disc 53 may also be driven by a rotary magnet 93, mounted on the bed plate 21 of the machine, FIGS. and 11. The transmission of the torsional move ment to the cam disc 53 takes place through a gear drive 94 on the shaft of the rotary magnet 93 to a toothed sector 95 provided on the cam disc 53.

The cam disc 53 is under tension of a coil spring 96.

A pneumatic drive of the disc cam 53 is shown in FIG. 16. A fluid motor 98, controlled by an electromagnetic valve 97, is attached to a plate 99 arranged by means of distance pieces 100 on a base plate 101. The base plate 101 is secured to the table plate 103 by means of screws 102 and carries, in a bearing 104, the double armed lever 83 for operating the disc cam 53 over the roller 84. One of the arms of the lever 83 is connected with the piston rod 106 of the fluid motor 98 over a link 105. A disc 107 is mounted on the piston rod 106 and cooperates with a contact 108 in such a way, that the driving motor 86 can only start when the cam disc 53 is in a position shown in FIG. 5.

The operation of the sewing machine for sewing and trimming the threads is effected by means of a starting and stop device, which consists of a foot treadle 111 (FIG. 1) in the sewing machine 109 with a bed plate 21 carried by a frame 110. Two rods 112, 113, FIGS. 1, 19, 20, are linked to the foot treadle 111, whereat the rod 112 is connected with a shift lever 114 of the motor 86, while the presser foot rod 113, which is in a bushing 115 mounted in an oil tray 116, is connected with the device 117 for lifting the presser foot 92 and releasing the needle thread tension 118, said device being mounted in the sewing machine 109.

The cranked motor rod 112 (FIG. 20) is slidable supported in a guide bearing 119 pivoted on the foot treadle 111. Screwed to the presser foot rod 113, by means of a screw 121, is an entrainment means 120, which is slidably supported on the motor rod 112. Between the olfset part of the motor rod 112 and the entrainment means 120 there is provided a tension spring 122. The presser foot rod 113 is provided on its upper end with a pressure plate 123 for the lifting mechanism of the presser foot 117.

The operation of the above described thread trimming device is as follows:

By pressing the foot treadle 111 forward from a neutral position the shift lever 114 for engaging the sewing drive will be actuated, whereby the pressure foot rod 113, resting with its pressure plate 123 on the bushing 115 in the oil tray 116, remains ineffective in the neutral position, while the tension spring 122 will be stretched. For the purpose of trimming the threads, the sewing drive will be disconnected by releasing the foot treadle 111 into the neutral position. By pressing the foot treadle 111 backwards the needle thread tension 118 will be released and then the presser foot 92 will be lifted by means of the presser foot rod 113 and the device 117 for lifting the presser foot 92 and by means of the motor rod 112 and the shift lever 114, the lifting magnet 82, the rotary magnet 93 or fluid motor 98 and the driving motor will be switched on. In cooperation with a synchronizing device 124 arranged on the main drive shaft 25, FIG. 17, the driving motor 86 will bring the needle 26 into high position during the motional action of thread trimming already described. By pressing the foot treadle 111 further backwards the presser foot 92 will be lifted for removing the work piece.

A direct drive of the cam disc 53 by the starting and stop device of the sewing machine is shown as a further form of construction in FIGS. 17 and 18. Apart from the above described rods 112, 113 a further rod 125 is required in this construction, the lower end 125 of which is provided with a collar 127, slidably guided in a tube 126 pivoted on the left side of the foot treadle 111. On its other end, the rod 125 is slidably guided in a bushing 128, mounted in the oil tray 116. A plunger with a bore 129 is slidably guided on the rod 125. Between the plunger 130 and a setting ring 132 there is arranged a pressure spring 131. Pivoted on the table plate 103 is a one-armed lever 134 .which rests on the plunger 130 and which, as described above, is in effective connection with the cam disc 53 by means of the roller 84.

The operation of this device is as follows:

By pressing the foot treadle 111 forwards the driving motor 86 will be coupled over the motor rod .112 and the shift lever 114. Hereby the tube .126 will slide downwards on to the end 125' of the rod 125, whereby the setting ring 132 will rest on the bushing 128. After releasing the foot treadle 111 into neutral position, as shown in FIG. 18, the sewing machine will stop, with the needle 26 in its downward position (FIG. 5). By pressing the foot treadle 11.1 backwards the lever 134 will be pressed against the roller 84 over the setting ring 132, the pressure spring 131 and the plunger 130. A torsional moment will be carried out upon the cam disc 53, as already described. Simultaneously the needle thread tension 118 will be released over the presser foot rod 113 and the pressure plate 123; the presser foot 92 will be lifted and the shift lever 1414 of the motor 86 will be operated, through the motor rod .112, thus bringing the needle 26 slowly into high position during the trimming operation.

It is possible to use a clutch driving motor instead of a positioning motor. In this case the sewing machine, after disconnecting the driving motor 86, may be stopped by hand in a downward position of the needle and by treading the foot treadle 111 backwards and loosening the brake of the motor, the needle 26 is brought manually into a high position during the trimming operation.

In a further form of construction, shown in FIGS. 12 to 14, the thread trimming device is installed in a work supporting arm sewing machine 135, having a proportionally small work supporting arm 136 in its sewing zone. The looper shaft 137, carrying the looper 32, is in driving connection with the loop taker drive shaft 138 over a pair of gear wheels 139. The shaft 138 is driven by an arm shaft (not shown) over a toothed belt 140 and a toothed belt wheel 1 41. Secured to the looper drive shaft 138 is the cam disc 66 provided with the control face 65, against which can abut the roller 64 of the rocker arm 62, pivoted on the axle 63 mounted in the work supporting arm 136. The other roller 61 of the rocker arm 62 is connected with the cam disc 53 formed with a toothed segment 95 and pivoted on the axle 56 fastened in the work supporting arm 136.

The roller 84, pivoted to the cam disc '53, is positioned adjacent to a double-armed lever 142 pivoted in the work, supporting arm 136. The one arm of the lever 142 protrudes from the work supporting arm 136 in order to be operated by the rotary magnet 93, the lifting magnet 82, the fluid motor 98 or mechanically for transmitting a torsional movement to the cam disc 53. The driving of the carrier 40 with the arcuate blade 42 which cooperates with the stationary cutting blade 77 and the bafile 78, is effected by means of an intermediate shaft 143 running parallel to the looper shaft .137 and carrying two gear wheels 144, 145 whereas the gear wheel 144 mates with the gear wheel 95 of the cam disc 53 and the gear wheel 1'45 mates with the gearing '51 of the carrier 40. A setting ring 147 is fastened to the intermediate shaft 143 for taking up one end of a coil spring 147 disposed on the shaft 143. The other end of the coil spring 147 is held by a wall of the work supporting arm 136.

What we claim is:

1. In combination with a lockstitch sewing machine provided with stitch forming elements including: a reciprocating needle driven by an arm shaft, a looper shaft in driven connection with said arm shaft, a cylindrical rotatable looper mounted on said looper shaft and provided with a needle thread seizing beak, a bed plate, a presser foot, a throat plate arranged above said looper within said bed plate, a feed dog within said throat plate, means for actuating said feed dog including a feed dog lifting shaft, and a theread tension release for the needle thread: thread trimming means for the needle thread and the looper threader comprising an arcuate blade, a stationary cutting knife engageable by said arcuate blade to sever said looper and needle threads when said needle is in an upper position, said arcuate blade being mounted on a carrier pivoted on said looper shaft and arranged in close proximity to the outer surface of said looper for concentric oscillation about said looper, driving and stop means for said sewing machine and actuating means for said driving, stop and thread trimming means, said carrier being in driven connection with a first cam disc controlled by said actuating means, a second cam disc secured to said feed dog lifting shaft and cooperating with said first cam disc for actuating said first cam disc for drawing off the thrwd from the bobbin, cutting the threads and blocking the thread trimming means and said stitched forming elements.

2. In the combination as claimed in claim 1, a rocker arm pivoted in said bed plate and provided with rollers abutting against said cam discs.

3. The combination claimed in claim 1, wherein said first cam disc is in driven connection with said carrier for said arcuate blade and pivoted on an axle, said first cam disc having a hollow for receiving one of said rollers of said rocker arm to keep it out of the field of action of said second cam disc during the operation of the sewing machine.

4. In the combination as claimed in claim 1, wherein said second cam disc is provided with a control face for influencing the movement of said first cam disc, said first cam disc being provided with a control face for preventing a jerky drawing off of said bobbin thread from said bobbin by said arcuate blade while performing a torsional moment to said first cam disc in interaction with said control faces.

5. In the combination as claimed in claim 1, wherein a rocker arm is pivoted in said bed plate and provided with rollers is in operative connection with said cam discs, said second cam disc being formed with a recess on its control face for collapsing of one of said rollers into said recess, a control face section on said first cam disc for imparting an accelerated movement to said arcuate blade during the cutting action in cooperation with said second cam disc.

6. In the combination as claimed in claim 1, a rotary magnet for driving said first cam disc, said rotary magnet being controlled by said stop means of said sewing machine, a gear drive between said rotary magnet and said first cam disc, said rotary magnet being mounted on said sewing machine.

7. In the combination as claimed in claim 6, biasing spring means for said first cam disc for leading back said cam disc into its normal position.

8. In the combination as claimed in claim 1, driving means for said first cam disc, a pin secured to said first cam disc and a lever controlled by said stop means of said sewing machine, said lever being in driving connection with said pin.

9. In the combination as claimed in claim 1, wherein said first cam disc is in driving connection with a lever pivoted below the bed plate of said sewing machine, a foot treadle for the driving motor, a two-piece connecting rod linking said lever and said foot treadle for varying the pressure upon said first cam disc by moving back said foot treadle.

10. In the combination as claimed in claim 1, wherein said first cam disc is in driving connection with a lever pivoted below the bed plate of said sewing machine, a foot treadle, a two-piece flexible connecting rod between said lever and said foot treadle to actuate said driving means of said sewing machine, to said foot treadle and connected with means, for lifting said presser foot and for releasing said needle thread tension by moving backwards said foot treadle, for loosening the needle thread tension for lifting said presser foot.

11. In the combination as claimed in claim 1, a bafile secured to said bed plate and cooperating with said arcuate blade for securing the engagement of the knife edge on said arcuate blade during cutting off said threads.

12. In the combination as claimed in claim 11, wherein said arcuate blade is provided with a groove for receiving said threads during its withdrawal from the supply of threads, said groove terminating in a clearance provided with a sharpened edge for cooperating with said stationary cutting knife.

13. In the combination as claimed in claim 1, wherein said carrier for said arcuate blade is of cup-shaped form, a ball-bearing bracket in which said carrier is pivoted, an oil retainer arranged in said bearing bracket and surrounding said looper shaft.

14. In combination with a lockstitch sewing machine provided with stitch forming elements including a reciprocating needle driven by an arm shaft, a looper shaft in operable connection with said arm shaft, a cylindrical rotating looper mounted on said looper shaft and provided with a needle thread seizing beak, a workpiece supporting arm, a throat plate mounted above said looper within said supporting arm and provided with a thread tension release for the needle thread: thread trimming means for said needle thread and the looper thread, comprising an arcuate blade, a stationary cutting knife engageable by said arcuate blade to sever said looper and needle threads when said needle is in an upper position, said arcuate blade being mounted on a carrier pivoted on said looper shaft and arranged in close proximity to the outer surface of said loopers for concentric oscillation about said looper, driving and stop means for said sewing machine and actuating means for said driving, stop and thread trimming device, said carrier being in driven connection with a first cam disc controlled by said actuating means, a second cam disc secured to said looper shaft, a rocker arm provided with rollers, said first cam disc, said second cam disc and said rocker arm arranged in the rear part of said supporting arm operably engaging with each other, an intermediate shaft pivoted in said supporting arm and provided with gear wheels on each of its ends for meshing with the teeth of said carrier and with the teeth of said first cam disc, said rollers pivoted on said rocker arm and abutting against said first and second cam discs, said rocker arm serving for transferring the rotational movements of said first cam disc to said carrier of said arcuate blade in dependence upon the position of said second cam disc, to draw off said looper thread from the bobbin, for trimming said threads and for blocking said thread trimming means and said stitch forming elements,

, a biasing spring mounted on said intermediate shaft for returning said first cam disc into its normal position.

References Cited UNITED STATES PATENTS HERBERT F. ROSS, Primary Examiner.

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