Shortening of needle thread end at the beginning and end of sewing in lockstitch sewing machines

In a process and a device for shortening the needle thread end at the beginning of sewing and at the end of sewing in two-thread lockstitch sewing machines, the catch thread device (23) of an already existing thread-cutting device (22; 60; 90) is moved into its thread-catching position during the first stitch formation cycle, and it is ensured, either by the selection of a suitable point in time for moving the catch thread device (23) or by a compressed air flow discharged from a compressed air line (81), that at least the reserve-side leg of the needle thread loop will be caught by the catch thread device (23). Part of the needle thread end is cut off during the return movement of the catch thread device (23) into its starting position. Furthermore, the needle thread is clamped either under a leaf spring (44), or is pushed by a sufficiently large feed step under the pressure foot, and is thus held in a frictionally engaged manner.

FIELD OF THE INVENTION 
The present invention relates to a process for shortening an end of a 
needle thread at a beginning of the seam to be formed for a two-thread 
lock stitch sewing machine as well as a device for carrying out the 
process including a sewing machine having a needle bar with a 
thread-guiding needle, a hook arranged under a needle plate cooperating 
with the needle to form stitches, a pressure foot, a feed mechanism and a 
thread-cutting device. 
BACKGROUND OF THE INVENTION 
In many sewing operations, especially in the clothing industry, the thread 
ends of a seam shall be on the underside of the fabric sewn or on the 
inner side of an article of clothing in order to achieve an attractive 
appearance of a seam. This requirement is satisfied by the use of 
correspondingly designed thread-cutting devices, which cut the needle 
thread and the hook thread under the needle plate. It must be ensured at 
the beginning of sewing that the loose needle thread end will be pulled 
onto the underside of the fabric being sewn during the first stitch 
formation cycle. In order for a secure connection of the needle thread and 
hook thread to be able to take place at the beginning of a sewing process, 
a reserve-side needle thread end of sufficient length must be left at the 
end of the seam formed previously during the thread-cutting process. 
However, this long needle thread end, which is necessary for reliable 
sewing-on, leads in turn to the formation of so-called bunches of threads 
of unattractive appearance on the underside of the fabric being sewn at 
the beginning of the seam. Since such thread bunches are unacceptable in 
many sewn products, especially those of high quality, these must 
subsequently be removed in a separate, relatively time-consuming 
operation. 
This disadvantage is eliminated in a stitch group sewing machine known from 
German Patent No. DE-PS 289,806 by providing a device for shortening the 
needle thread end at the beginning of sewing in addition to the 
thread-cutting device. This additional device has a catch thread arm, 
which ends in a catching hook and is attached to a support wheel of the 
thread-cutting device, which support wheel is rotatable around a vertical 
axis and carries two cutting knives. A spring-loaded thread clamp, which 
is normally open, and by which a cam surface designed at the catch thread 
arm can be closed, is arranged on the underside of the needle plate. A 
rotary movement, which is opposite the rotary movement taking place at the 
beginning of a thread-cutting process, is imparted to the support wheel at 
the beginning of a sewing process. Due to this rotary movement, the thread 
catch arm introduces the needle thread end, which was pulled under the 
needle plate during the first stitch, into the opened thread clamp. During 
the further movement of the catch thread arm, the thread clamp is then 
closed via the cam surface, and the section of the needle thread end 
projecting beyond this cam surface is finally cut off, while the catching 
hook cooperates with a separate knife. After forming two stitches, the 
catch thread arm is pivoted back into the starting position, and the 
thread clamp is again opened. 
Even though the technical expense required for embodying the device is 
reduced in the prior-art sewing machine due to the fact that the support 
wheel carrying the cutting knives of the thread-cutting device also 
carries the catch thread arm used to catch the needle thread end, it is 
now necessary to move the entire support wheel within a larger angle range 
than during the actual thread cutting in order to shorten the needle 
thread end, so that the drive mechanism also must be accordingly adapted. 
Therefore, the prior-art process is suitable for shortening the needle 
thread end mainly for stitch group sewing machines, in which the special 
drive movements of the support wheel can be brought about in a relatively 
simple manner by correspondingly designing the cam plate. 
SUMMARY AND OBJECTS OF THE INVENTION 
The primary object of the present invention is to provide a process and a 
device for shortening the needle thread end at the beginning of sewing, 
which process and device can be embodied with a small amount of technical 
expense. 
According to the invention, a process is provided for shortening the end of 
a needle thread at a beginning of the seam to be formed with a two-thread 
lock stitch sewing machine. The invention also includes a device for 
performing the process including a sewing machine having a needle bar with 
a thread guiding needle, a hook which cooperates with the thread-guiding 
needle and is arranged under a needle plate, a pressure foot, a feed 
mechanism and a thread-cutting device which contains a catch thread device 
with a catching element with a thread-catching area, the catch thread 
device being movable into a thread-catching position and a knife. The 
process includes the steps of moving the catch thread device into the 
thread-catching position prior to or during the first stitch formation 
cycle. At least a section of the reserved side leg of the needle thread 
loop, or the needle thread end is then positioned crossing the plane of 
the path of movement of the catch thread device within the thread-catching 
area of the catch thread device. The section of the needle thread end is 
then cut during a further or return movement of the catch thread device 
into the cutting position. The sewing machine is preferably provided with 
a hook doubly rotating around a horizontal axis and the thread-cutting 
device has a drive mechanism that can be switched on as a function of the 
movement process of the sewing machine. The drive mechanism of the 
thread-cutting device can be switched on at two different angle positions 
of the hook before performing the thread-cutting process taken place at 
the end of the seam and for performing the shortening of the end of the 
needle thread, which takes place at the beginning of the seam. An open end 
piece of a compressed air line may be arranged and oriented under the 
needle plate in an area of the hook such that the compressed air flow 
discharged from the end piece extends above the hook from its rear side in 
a direction of its front side and essentially in parallel to the axis of 
rotation of the hook. Both catching elements or at least the additional 
catching element is formed by a recess, a cutting edge, which cooperates 
with the knife, is associated with the additional catching element. 
By using the catch thread arm of a thread-cutting device already present to 
shorten the needle thread end, and to move it along the same path of 
movement as in the case of normal thread cutting, which takes place at the 
end of the seam, wherein either the reserve-side leg of the needle thread 
loop, or generally the needle thread end, rather than the fabric-side leg, 
is caught and fed to the cutter in this case according to the present 
invention, the shortening of the needle thread end can be performed in a 
relatively simple manner, i.e., an existing thread-cutting device can also 
be used to shorten the needle thread end at the beginning of sewing 
without an appreciable technical expense in new sewing machines and 
already existing sewing machines alike. 
According to future aspects of the invention it possible for the catch 
thread arm to catch the reserve-side leg of the needle thread loop or, if 
the thread loop is already untied, the needle thread end. To shorten the 
needle thread end at the beginning of sewing, it is necessary to move the 
catch thread arm into its catching position earlier than in the case of 
thread cutting at the end of the seam. 
According to a second possibility of catching the reserve-side leg of the 
needle thread loop or the needle thread, the catch thread device can be 
moved to shorten the needle thread end at the same relative point in time 
in relation to the hook position as in the case of thread cutting at the 
end of the seam, so that the drive for the catch thread arm can be 
actuated in the same manner. 
While the catch thread arm is moved into the catching position in the 
course of the first stitch formation cycle in the two processes mentioned 
immediately above, and correct coordination of the movement of the catch 
thread arm in time with the instantaneous position of the needle thread 
end or the needle thread loop is important for catching the needle thread 
end, or even an auxiliary means is needed for moving the needle thread end 
into a position in which it can be caught, highly reliable catching of the 
needle thread end is achieved according to another aspect of the invention 
due to the fact that the catch thread device, which is provided with a 
recess forming an additional catching element, is brought, before the 
needle first passes through the stitch hole of the needle plate, into a 
position in which the needle penetrates into the recess of the catch 
thread device, thus forcibly introducing the needle thread end into this 
recess and making it available to the additional catching element. 
In sewing machines in which the needle does not participate in the feed 
movement of the fabric being sewn, and the stitch hole of the needle plate 
can therefore be small, holding the needle thread end, which is necessary 
for the first concatenation of the shortened needle thread end with the 
hook thread, is brought about by the fabric being sewn being fed, after a 
section of the needle thread end has been cut off, to the extent that the 
section of needle thread located between the pressure foot and the needle 
plate is pulled out in the shape of a U in the horizontal direction, and 
is thus held in a frictionally engaged manner between the pressure foot 
and the top side of the fabric being sewn, as well as between the needle 
plate and the underside of the fabric being sewn. 
This manner of holding is impractical for needle feed sewing machines. 
Since the stitch hole in needle feed sewing machines is an elongated hole 
extending in the direction of feed, whose length depends on the greatest 
possible stitch length that can be set, the clamping effect would appear 
only after at least one additional feed step, and only after a plurality 
of feed steps in the case of small stitch length settings, namely, only 
when the section of the needle thread located within the fabric being sewn 
has been fed beyond the end of the stitch hole and has thus come to lie 
between the needle plate and the pressure foot sole. It is therefore more 
advantageous for needle feed sewing machines to hold the needle thread end 
by means of a thread clamp for connecting it to the hook thread. 
The division of the return movement of the catch thread device into two 
steps makes it possible to design or arrange the thread clamp associated 
with the catch thread device such that the needle thread end is held by 
the needle clamp only in the intermediate position of the catch thread 
device, and it is released after the further movement of the catch thread 
device or during its return into the starting position. This makes it 
unnecessary to associate the thread clamp with a closing and opening 
mechanism. 
According to a further aspect of the invention, the drive mechanism of the 
thread-cutting device can be turned on at two different angle positions of 
the hook. While it is advantageous for thread cutting at the end of the 
seam to move the catch thread device into its catching position only when 
the two legs of the needle thread loop have fallen off from the thread 
guide plate of the hook, and extend in different directions in relation to 
the stitch hole, so that the catch thread device catches only the 
fabric-side loop leg to obtain short thread ends on the fabric being sewn, 
it is advantageous, for shortening the needle thread end at the beginning 
of sewing, to move the catch thread device into its catching position at 
an earlier point in time, namely, at a time when the two loop legs are, 
or, if the needle thread loop is already untied, the needle thread end is 
still in contact with the thread guide plate of the hook, so that the 
catch thread device is also able to catch the reserve-side loop leg or the 
needle thread end. 
The use of a pneumatic cylinder as the drive mechanism for the 
thread-cutting device makes it possible to bring about different movements 
in time of the catch thread device in a particularly simple manner. 
The compressed air flow discharged from the compressed air line ending in 
the area of the hook not only brings the reserve-side loop leg or the 
needle thread end into a position in which the reserve-side loop leg or 
the needle thread end can be caught by the catch thread device, but it 
also blows the needle thread end cut off away from the area of the hook, 
thus preventing this thread section from being again caught by the hook 
and tied into the seam. 
Since the path of movement of the catching element of the catch thread 
device, which is used to catch the threads to be cut off at the end of the 
seam, is generally located at a greater distance from the stitch hole, it 
is suggested that an additional catching element, designed as a recess, be 
provided at the catch thread device, and this recess may also form the 
other catching element, if desired. 
Absolutely reliable catching of the needle thread by the catch thread 
device is guaranteed if the recess is designed as a hole according to 
claim 10. Since a hole has a lateral limiting wall that is closed in 
itself, the needle thread end, which is pulled under the needle plate 
during the first stitch formation process and then hangs down freely and 
in an uncontrolled manner either until it is introduced into a thread 
clamp or, if no thread clamp is present, until the first connection to the 
hook thread, cannot deviate to the side, as in the case of an, e.g., 
slot-like recess. 
Two alternative solutions for designing or arranging the cutting edge 
cooperating with the knife are disclosed. A first solution involves the 
edge area of the recess, which edge area is located on a top side of the 
catch thread device and is directed opposite knife, is designed as a 
cutting edge. According to a second solution the catch thread device is a 
cutting edge, which is designed on its top side and cooperates with the 
knife, in that a recess is connecting to the cutting edge via a 
thread-receiving groove. 
When a pneumatic cylinder is used as the drive mechanism, the position of 
the recess or hole is selected, such that the thread-catching position of 
the catch thread device is always the same for thread cutting at the end 
of the seam and for shortening the needle thread end at the beginning of 
the seam. 
Since the catch thread device must be moved into the thread-catching 
position for catching the needle thread at the beginning of a sewing 
process at a different point in time in relation to the hook position than 
for catching the needle thread and the hook thread at the end of a sewing 
process, for the case in which the drive mechanism of the thread-cutting 
device has a cam, that the catch thread device be associated with an 
additional drive mechanism, and that one of the gear members be designed 
as a spring-loaded gear member, e.g., in the form of a telescoping 
connecting rod as a result of which a restoring force builds up on 
actuation of the additional drive mechanism. Due to the spring-loaded 
design of one of the gear members, the cam can have a cam groove to be 
traced in a positive-locking manner, and the tracing member can remain in 
its relative tracing position in relation to the cam groove during the 
movement of the catch thread device into the thread-catching position, 
which takes place prior to the beginning of sewing. 
The restoring force acting on the gear member of spring-loaded design, 
which is generated during the forward movement of the catch thread device 
into the thread-catching position, which movement is brought about by the 
additional drive mechanism, makes it possible to design the additional 
drive mechanism as a pneumatic cylinder and to have it act on one of the 
gear members of the thread-cutting device only in a spring-actuated 
manner. After the piston rod of the pneumatic cylinder has withdrawn, the 
catch thread device is returned into its starting position in this case by 
the restoring force generated previously. 
According to a further aspect of the invention a locking member, which can 
be introduced into and removed from the path of movement of the catch 
thread device or the gear of the thread-cutting device, is provided to 
stop the catch thread device in an intermediate position. If a pneumatic 
cylinder is the drive mechanism of the thread-cutting device, this offers 
the advantage that the interruption of the movement of the catch thread 
device, which is brought about by the locking member being brought into 
the operating position, is completed without problems after withdrawal of 
the locking member, without the need to again trigger or switch on the 
drive mechanism. 
If, in contrast, the drive mechanism of the thread-cutting device contains 
a cam that can be driven by the sewing machine, it is advantageous, if the 
catch thread device is to be held in an intermediate position by a locking 
member that can be engaged and disengaged, to design, one of the gear 
members as a spring-loaded gear member, e.g., in the form of a telescoping 
connecting rod. A gear member of spring-loaded design makes it possible in 
this case not to have to interrupt the drive connection between the cam 
and the subsequent gear member cooperating with it during the engagement 
of the locking member, and to store the residual drive impulse originating 
from the cam by the tensioning of the spring element of the said gear 
member of spring-loaded design for returning the catch thread device into 
its starting position and to release it after disengagement of the locking 
member, after which the catch thread device is returned into its starting 
position by means of this spring element. 
If a needle thread clamp is associated with the thread-cutting device, 
which has a drive mechanism provided with a cam, the additional drive 
mechanism is to be designed such that it shall be able to move the catch 
thread device into two operating positions, one of them being the 
thread-catching position at the beginning of a sewing process, and the 
other being a thread-clamping position. 
The additional drive mechanism, which can be switched into two operating 
positions, is embodied by two pneumatic cylinders, which perform different 
effective strokes. This can be achieved. e.g., either by using two 
pneumatic cylinders with different stroke lengths, or by two pneumatic 
cylinders with equal stroke lengths acting on an interconnected lever at 
two points located at different radial distances from the axis of the 
lever. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its uses, reference 
is made to the accompanying drawings and descriptive matter in which 
preferred embodiments of the invention are illustrated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Exemplary Embodiment 1 
FIG. 1 shows the head 1 and the base plate 2 of a sewing machine. The 
needle bar 3, which is driven in the known manner and carries a 
thread-carrying needle 4, is arranged in the said head 1. A take-up lever 
5, likewise driven in the known manner, and a pressure bar 6, which 
carries a pressure foot 7, are also arranged in the said head 1. A 
prior-art thread wiper 8, of which only the wiper lever 9, made of wire, 
and the pneumatic cylinder 10 used to drive it, are shown, is arranged on 
the rear side of the said head 1. 
A hook drive shaft 11, which is in drive connection with a lower main shaft 
13 via a speed-increasing drive 12, is mounted in the said base plate 2. A 
doubly rotating two-thread lockstitch hook 15 is attached to the front end 
of the said hook drive shaft 11 under the said needle plate 14. The said 
hook 15 contains the hook body 16 with the hook tip 17 in the known 
manner. The thread guide plate 18 is attached on the circumferential side 
of the said hook body 16. A bobbin case holder 19 and a bobbin case 20 are 
inserted into the said hook body 16. 
The feed dog 21 of the feed mechanism of the sewing machine, is in drive 
connection with the said drive shaft 13 in a known manner, and is 
therefore not shown. This consequently performs rectangular movements and 
extends above the said hook 15. 
A thread-cutting device 22 is arranged under the said base plate 2. The 
said thread-cutting device 22 has a catch thread device 23, which is 
arranged coaxially with the said hook 15, and is in its starting position 
in FIG. 2. The said catch thread device 23 is attached to an arm 24 of a 
sleeve 25, which is rotatably mounted on a bearing bush 26 of the said 
hook drive shaft 11. A connecting rod 27, which is connected to a 
longitudinally adjustable arm 28 of an angle lever 29, which latter is 
carried by a bearing block 30 that is an integral part of the housing, is 
hinged to the said arm 24. The other arm 31 of the said angle lever 29 is 
connected to the piston rod 33 of a pneumatic cylinder 34 via a connecting 
rod 32. The design and the control circuit of the said pneumatic cylinder 
34 correspond to the pneumatic cylinder and the pneumatic cylinder control 
circuit for a thread-cutting device, which are disclosed in DE 32,44,996 
C2. 
The said catch thread device 23 has a separating tip 35 (FIG. 4), designed 
at the free end, and a thread-catching barb 36, which is directed in the 
opposite direction. A flat groove 37, which opens into a continuous 
elongated hole 38, is designed at the foot of the said barb 36. The edge 
39 of the said elongated hole 38 located adjacent to the said separating 
tip 35 is designed with sharp edges, and is used as a cutter. The front 
section of the said catch thread device 23 between the said separating tip 
35 and the said edge 39 is designated by 40. A cutting knife 42, whose 
cutting edge 43 (FIG. 3) is in contact with the top side of the said catch 
thread device 23 and cooperates with the said edge 39, is attached to a 
projection 41 (FIG. 2) of the said base plate 2. 
A leaf spring 44, which projects above the said cutting edge 43 and ends in 
a bent end or clamp piece 45, which extends into the path of movement of 
the said catch thread device. The leaf spring 44 is attached to the said 
projection 41 above the said cutting knife 42. Together with the said 
section 40 of the said catch thread device 23, the said leaf spring 44 
forms a thread clamp 46 (FIG. 12). 
A pneumatic cylinder 48, whose piston rod 49 carries a stop plate 50 acting 
as a locking member, is arranged under the said hinge 47 between the said 
connecting rod 27 and the said arm 28 of the said angle lever 29. 
The said above-described thread-cutting device 22 differs from the 
thread-cutting device disclosed in DE 32,44,996 C2 cited only by the fact 
that the said leaf spring 44 and the said pneumatic cylinder 48 with the 
said stop plate 50 are additionally provided in it. 
Mode of Operation 
The mode of operation of the said thread-cutting device during thread 
cutting at the end of a sewing process is the same as that of the 
thread-cutting device according to DE 32,44,996 C2, so that this function 
need not be explained in greater detail. It should only be pointed out 
that the said catch thread device 23 is moved in this case from its 
starting position into the thread-catching position only when the said 
thread guide plate 18 has already withdrawn from the two legs NN and NV of 
the needle thread loop, or the legs NN and NV have already fallen off from 
the said thread guide plate 18. This point in time is of significance 
because, in the case of a two-thread lockstitch rotary hook doubly 
rotating around a horizontal axis, the fabric-side loop leg NN is moved 
past the front side of the bobbin case 20, and the reserve-side loop leg 
NV is moved past the rear side of the said bobbin case holder 19, and the 
two legs NN and NV thus extend at different angles to the said stitch hole 
51 of the said needle plate 14 after falling off from the said thread 
guide plate 18. In the case of this thread course, the said catch thread 
device 23 with its said separating tip 35 is able to pass reliably through 
between the two loop legs NN and NV, and the fabric-side loop leg NN is 
caught by the said barb 36, is fed to the said cutting knife 42 during the 
return movement of the said catch thread device 23, and the reserve-side 
loop leg NV is kept away from the said cutting knife 42. By cutting off 
the fabric-side loop leg NN, a short needle thread end is obtained on the 
fabric in the area of the end of the seam, as desired, on the one hand, 
and, on the other hand, a long reserve-side needle thread end, which is 
necessary for reliably connecting the needle thread end to the hook thread 
at the beginning of the next sewing process, is obtained. The additional 
term "needle thread end," which is designated by the reference numeral NE, 
is defined here as the thread section extending to the actual end E of the 
needle thread. 
At the beginning of a sewing operation carried out at reduced speed, the 
said needle 4 pulls part of the loose needle thread end NE through the 
said stitch hole 51 in the downward direction (it is achieved due to the 
said thread wiper 8 that the said needle thread end NE will not come under 
the said pressure foot 7 and will not be held by it), after which the 
needle thread end NE is caught by the said hook tip 17 and is moved as a 
thread loop around the bobbin housing formed by the said bobbin case 
holder 19 and the said bobbin case 20. As was mentioned, the reserve-side 
loop leg NV now extends behind the said bobbin case holder 19, while the 
other loop leg, which leads to the end E of the needle thread, extends on 
the front side of the said bobbin case 20. This loop leg is comparable to 
the loop leg that forms the fabric-side loop leg NN after the first stitch 
formation. The loop leg leading to the actual end E is therefore also 
designated by NN. 
It should be mentioned here that a certain frictional force is exerted on 
the needle thread introduced into the fabric during the first stitch 
formation cycle in the case of thick and firm fabrics. Due to this 
frictional force, the loop leg NN leading to the end E is held after the 
needle thread loop has been caught by the said hook tip 17, while the said 
hook 15 pulls in thread from the slack thread formed by the said take-up 
lever 5 through the needle groove during the time during which the said 
needle 4 is penetrated into the fabric. As is shown in FIGS. 8 through 11, 
the said hook 15 is thus able to form a complete needle thread loop 
already during the first stitch formation cycle. 
In contrast, a much lower frictional force is exerted on the needle thread 
in the case of thin and looser fabrics. This causes the said hook 15 to 
pull downward not only thread from the slack thread formed by the said 
take-up lever 5, but at the same time also the free end E of the needle 
thread, so that only a small thread loop can be formed, and this small 
thread loop is already untied in the hook positions shown in FIGS. 8 
through 11. After untying of the needle thread loop, the needle thread end 
NE extends hanging down freely under the said needle plate 14, and is in 
the same position as a reserve-side loop leg NV, namely, behind the said 
bobbin case holder 19. Since the conditions occurring during the catching 
of a freely hanging needle thread end NE by the said catch thread device 
23 are the same as during the catching of the reserve-side loop leg NV, 
the further course of the function will be explained only on the basis of 
the situation in which the needle thread loop is still present at the time 
of catching of the thread. 
In the rotary position of the said hook 15 shown in FIG. 8, in which the 
end part of the said thread guide plate 18 is still in the area of the 
said stitch hole 51, and both loop legs NN and NV are consequently in 
contact with the said thread guide plate 18 next to each other, pressure 
is admitted to the said pneumatic cylinder 34, and, as a consequence of 
this, the said catch thread device 23 is moved from its starting position 
into the thread-catching position shown in FIGS. 8 and 9, in which the 
said barb 36 is located in front of the two loop legs NN, NV. After the 
said catch thread device 23 has reached its thread-catching position, 
pressure is admitted to the said pneumatic cylinder 48, and the said stop 
plate 50 is moved into an upper position, in which it is thus in the path 
of pivoting movement of the said hinge 47. 
During the further course of the movement of the said needle thread loop 
around the bobbin housing, the end E of the needle thread is pulled under 
the said needle plate 14, after which the thread loop is untied, and the 
now freely hanging needle thread end NE is in contact with the said catch 
thread device 23 only by the thread section that formed the previous 
reserve-side loop leg NV. 
The sewing machine briefly stops in the top dead center of the said take-up 
lever 5 during this first stitch formation cycle, and the said catch 
thread device 23 is returned by the said pneumatic cylinder 34 in the 
direction of its starting position, while it carries the needle thread end 
NE and pulls it under the said end piece 45 of the said leaf spring 44. 
The said stop plate 50, located in the path of pivoting movement of the 
said hinge 47, causes the said catch thread device 23 not to be able to 
have been completely withdrawn into its starting position at this point in 
time, but to stop in the position shown in FIG. 12, in which its said 
front section 40 is located under the said end piece 45, forms the said 
thread clamp 46 together with it, and the said edge 39 is still at a 
spaced location from the said cutting edge 43 of the said cutting knife 
42. In this position of the said catch thread device 23, the needle thread 
end NE arriving from the said stitch hole 51 extends between the said end 
piece 45 and the said front section 40 of the said catch thread device 23, 
and is clamped between them. From this point of clamping, the needle 
thread end NE then extends under and through the said cutting edge 43, 
beyond the said slotted hole 38, and through the said groove 37, after 
which it hangs down freely from the foot of the said barb 36. 
Since the said angle lever 29 is coupled with the said piston rod 33 of the 
said pneumatic cylinder 34 in a positive-locking manner, its piston, not 
shown, is also prevented by the said stop plate 50 from moving into its 
end position. 
After the needle thread end NE has been introduced into the said thread 
clamp 46, the sewing machine performs the second stitch formation cycle. 
Pressure is admitted to the said pneumatic cylinder 34 during this time, 
as a result of which the said hinge 47 is maintained in contact with the 
said stop plate 50, and the said catch thread device 23 is maintained in 
the thread-clamping position. Since the needle thread end NE is held 
during the second stitch formation cycle, the said hook is able to pull 
out a complete needle thread loop, lead it around the bobbin housing, and 
catch the free end of the hook thread G. The needle thread loop is then 
withdrawn by the subsequent upward movement of the said take-up lever 5, 
and the first connection of needle thread and hook thread is tightened in 
the fabric being sewn. 
The sewing machine is again stopped briefly at the top dead center during 
the second stitch formation cycle, and the said pneumatic cylinder 48 is 
then reversed, as a consequence of which it pulls the said stop plate 50 
out of the path of pivoting movement of the said hinge 47. As a 
consequence, the piston, not shown, of the said pneumatic cylinder 34, 
which continued to be pressurized, is returned into its end position, and 
the said catch thread device 23 is pivoted back into its starting position 
according to FIGS. 2 and 3. Part of the needle thread end NE is now cut 
off due to the cooperation of the said cutting edge 43 and the said edge 
39. The needle thread end, shortened after thread cutting at the beginning 
of the seam, has the same length as the thread ends that remain on the 
fabric after the thread cutting performed at the end of the seam. 
So-called thread bunches at the beginning of the seam are reliably avoided 
by the shortening of the needle thread end at the beginning of the seam. 
Exemplary Embodiment 2 
In the second exemplary embodiment shown in FIG. 5, the design of the 
sewing machine, including the hook, is identical to that of the first 
exemplary embodiment, so that identical components are designated by the 
same reference numerals. This also applies to the thread-cutting device 
designated by reference numeral 60, i.e., its design from the said catch 
thread device 23 up to and including the said angle lever 29 is identical 
to that of the said thread-cutting device 22. Furthermore, the said 
thread-cutting device 60 also has a said leaf spring 44, which is arranged 
above the said cutting knife 42 and forms a thread clamp together with the 
said catch thread device 23, which is in a defined position. Finally, as 
in the first exemplary embodiment, a said pneumatic cylinder 48, which 
carries a said stop plate 50, is associated with the said hinge 47 of the 
said angle lever 29. 
The drive for the said catch thread device 23 is derived, similarly to that 
described in DE 38,19,135 C1, from a cam 61, which is attached to the said 
main shaft 13 and has a control groove 62 and a control segment (63). An 
axially displaceable shaft 64 is arranged in parallel to the said main 
shaft 13. A control lever 66, provided with a roller pin 65, and a release 
lever 67 are attached to the said shaft 64. A detent pawl 69 is mounted 
freely rotatably on a bearing bush 68 of the said shaft 64. A spring 70, 
which is wound around the said shaft 64, and is in contact with the said 
control lever 66 at one end and with the said detent pawl 69 at the other 
end, causes the said detent pawl 69 to pivot in the direction of the said 
control segment 63 and the said roller pin 65 to pivot out of the said 
control groove 62. At the same time, the said spring 70 acts as a 
compression spring and displaces the said shaft 64 into the right-hand end 
position shown in FIG. 5, in which the said roller pin 65 is located 
opposite the said control groove 62 when the needle of the sewing machine 
is in its deep position. 
A spring-loaded starting lever, not shown, which can be actuated by an 
electromagnet, likewise not shown, is associated with the said release 
lever 67. The design and the arrangement of the said starting lever 
correspond to those of the starting lever of the prior-art thread-cutting 
device according to DE 38,19,135 C1. 
A locking piece 71 is fastened to the side of the said control lever 66 
located in its right-hand end position; the said locking piece 71 is 
designed and arranged such that it forms an axially acting movement 
barrier for the said control lever 66 only in the resting position of the 
said control lever 66 that is remote from the said cam 61, but the said 
control lever 66 pivoted into its operating position is able to move under 
it. 
At the end of the said shaft 64 facing the said hook 15, a carrier piece 72 
is mounted rotatably, but in an axially fixed position. The said carrier 
piece 72 is connected to the said arm 31 of the said angle lever 29 via a 
telescoping connecting rod 73. The said telescoping connecting rod 73 has 
a bar 74, which is hinged to the said angle lever 29 at one end, is 
provided with threads at its other end, and is screwed together with a 
sleeve 75 of corresponding design. A piston-like stop piece 76, which is 
attached to one end of a bar 77 passing through the bottom of the said 
sleeve 75, is accommodated in the said sleeve 75. The other end of the 
said bar 77 is hinged to the said carrier piece 72. A transversely 
projecting pin 78, which passes through an elongated hole 79 in the said 
sleeve 75, is arranged in the said stop piece 76. A compression spring 80 
arranged in the said sleeve 75 holds the said stop piece 76 in the 
starting position shown in FIG. 5, in which the said pin 78 is in contact 
with the left-hand end of the said elongated hole 79. 
A compressed air line 81, which has an open end piece 82 located above the 
said hook 15, is laid under the said base plate 2. The section of the said 
compressed air line 81 located in front of the said end piece 82 extends 
essentially in parallel to the axis of rotation of the said hook, so that 
a compressed air flow discharged from the said end piece 82 is also 
directed essentially in parallel to the axis of rotation of the said hook, 
and extends to the left in the direction of its front side from the rear 
side of the said hook 15 according to FIG. 5. 
Mode of Operation 
Because of the rigid association of the said cam 61 with the said main 
shaft 13, the said catch thread device 23 in the exemplary embodiment 
according to FIG. 5 can be moved into its thread-catching position only in 
the same relative rotary position of the said hook 15 during the two 
different cutting processes, i.e., during both thread cutting at the end 
of the seam and shortening of the needle thread end at the beginning of 
sewing. 
Since it is necessary, during thread cutting at the end of the seam, for 
the said catch thread device 23 to catch only the fabric-side leg of the 
needle thread loop, the said catch thread device 23 is moved from its 
starting position into the thread-catching position, as was explained in 
the first exemplary embodiment, only when the said thread guide plate 18 
has already withdrawn from the two legs NN and NV of the needle thread 
loop, and these [legs] extend at different angles in relation to the said 
stitch hole 51, the fabric-side loop leg NN extending on the front side of 
the said bobbin case 20 and the reserve-side loop leg NV extending on the 
rear side of the said bobbin case holder 19. 
Since, in contrast, the reserve-side loop leg NV is to be caught and fed to 
the said cutting knife 42 for shortening the needle thread end at the 
beginning of sewing, it must be ensured in the second exemplary embodiment 
that the reserve-side loop leg NV will be in a position suitable for 
catching despite the dropping off of the said thread guide plate 18. To 
achieve this, compressed air is fed into the said compressed air line 81 
with the beginning of the first stitch formation cycle. The compressed air 
flow discharged from the said end piece 82 now presses the reserve-side 
loop leg NV, after it drops off from the said thread guide plate 18, in 
the direction of the front side of the said hook 15, and the intensity of 
the compressed air flow is selected to be such that the reserve-side loop 
leg NV will assume essentially the same position in the area of the path 
of movement of the said catch thread device 23 as it does at the time when 
both loop legs NN and NV are still in contact with the said thread guide 
plate 18. 
To shorten the needle thread end at the beginning of sewing, the sewing 
machine is briefly stopped during the first stitch formation cycle with 
the needle in the deep position. In this position of the sewing machine, 
the said control groove 62 of the said cam 61 assumes a position in which 
the said roller pin 65 can be moved into the said control groove 62 by a 
simple pivoting movement of the said control lever 66. 
By actuating a switch during the pressing of the foot pedal of the sewing 
direction in the reverse direction, the electromagnet associated with the 
said thread-cutting device 60 is briefly switched on, and the drive motor 
of the sewing machine is then turned on again. Via the starting lever, not 
shown, and the said release lever 67, the said control lever 66 is pivoted 
by the said electromagnet, and the said roller pin 65 is pivoted into the 
said control groove 62. At the same time, the said spring 70 pivots the 
said detent pawl 69, which will then secure the position of the said 
control lever 66 pivoted into the operating position. 
During the following revolution of the said main shaft 13, an obliquely 
extending section of the said cam 62 displaces the said shaft 64 from the 
starting position according to FIG. 5 to the left via the said control 
lever 66. This movement is transmitted via the said telescoping connecting 
rod 73 onto the said angle lever 29, as a consequence of which the said 
catch thread device 23 moves from its starting position into the 
thread-catching position shown in FIGS. 10 and 11. As was explained above, 
the movement of the said catch thread device 23 takes place at a time at 
which the said thread guide plate 18 has already withdrawn from the two 
loop legs NN and NV. However, the compressed air flow being discharged 
from the said end piece guarantees that the two loop legs NN and NV will 
be located on the side of the said catch thread device 23, on which the 
said barb 36 is located. After the said catch thread device 23 has reached 
its thread-catching position, pressure is admitted to the said pneumatic 
cylinder 48, and the said stop plate 50 moves into an upper position, in 
which it will be in the path of pivoting movement of the said hinge 47. 
During the further course of the looping movement of the needle thread loop 
around the bobbin housing, the end E of the needle thread is pulled under 
the said needle plate 14, after which the needle loop leg is untied, and 
the needle thread end NE is in contact with the said catch thread device 
23 only by the thread section which formed the previous reserve-side loop 
leg NV. 
The said control groove 62 is designed such that at the time of the top 
dead center of the said take-up lever 5, it will have moved the said catch 
thread device 23 back in the direction of its starting position. The 
needle thread end NE is carried by the said hook 36 and pulled under the 
said leaf spring 44 by the return movement of the said catch thread device 
23. 
The said stop plate 50, which is located in the path of pivoting movement 
of the said hinge 47, causes the said catch thread device 23 to be unable 
to be completely withdrawn into its starting position at this point in 
time, but to stop, in the same manner as in the first exemplary 
embodiment, in the position shown in FIG. 12, and to hold the needle 
thread end NE clamped. 
Since the said control lever 66 is in positive-locking connection with the 
said cam 61 during the engagement of the said roller pin 65 in the said 
control groove 62, the said control lever 66 is pushed back into its 
starting position despite the said stop plate 50 being in the path of 
pivoting movement of the said hinge 47. The said bar 77 with the said stop 
piece 76 is now displaced in relation to the fixed sleeve 75, as a result 
of which the said compression spring 80 is tensioned. 
By the end of the return movement of the said control lever 66, the said 
control segment 63 pivots the said detent pawl 69, as a result of which 
the said starting lever, not shown, is released, and returns into its 
starting position. As a result, the said spring 70 is able to push the 
said control lever 66 away from the said control groove 62. In this 
position of the said control lever 66, the said tensioned compression 
spring 80 holds the said control lever 66 in lateral contact with the said 
locking piece 71. 
After the needle thread end NE has been introduced into the said thread 
clamp 46, the sewing machine performs the second stitch formation cycle. 
The said tensioned compression spring 80 causes the said hinge 47 to be 
held in contact with the said stop plate 50 and the said catch thread 
device 23 to be held in the thread-clamping position. Since the needle 
thread end NE is fixed during the second stitch formation cycle, the said 
hook 15 is able to pull a complete needle thread loop, to lead it around 
the bobbin housing, and to catch the free end of the hook thread G. The 
needle thread loop is then withdrawn by the subsequent upward movement of 
the said take-up lever 5, and the first thread connection is tightened by 
the needle thread and the hook thread in the fabric being sewn. 
The sewing machine is again stopped briefly at the top dead center of the 
said take-up lever 5 during the second stitch formation cycle, and the 
said pneumatic cylinder 48 is then reversed, as a consequence of which it 
pulls the said stop plate 50 out of the path of pivoting movement of the 
said hinge 47. As a consequence of this, the said compression spring 80 
moves the said sleeve 75 back into the end position shown in FIG. 5, and 
pivots the said catch thread device 23 into its starting position. Part of 
the needle thread end NE is now cut off in the same manner as in the first 
exemplary embodiment. The thread section cut off is blown away from the 
said hook 15 by the air flow that still continues to be discharged from 
the said end piece 82, so that this thread section is reliably prevented 
from being accidentally sewn in during one of the subsequent stitch 
formation processes. To accomplish this additional function. the 
compressed air supply is stopped only after expiration of an adjustable 
time after the shortening of the needle thread end. 
The air flow also has the further advantageous effect that it keeps the 
loose hook thread end out of the catching area of the said barb 36 during 
the pivoting of the said catch thread device 23 into the thread-catching 
position. Based on these advantageous additional effects of the air flow, 
it may be advantageous to provide a compressed air line comparable to the 
said compressed air line 81 in the first exemplary embodiment as well. 
Exemplary Embodiment 3 
In the third exemplary embodiment shown in FIGS. 6 and 7, the design of the 
sewing machine, including that of the said hook, is identical to that of 
the first exemplary embodiment, so that identical components are 
designated by the same reference numerals. 
The thread-cutting device 90 is identical to the corresponding parts of the 
said thread-cutting device 22 in terms of the arrangement of the catch 
thread device and the design of the drive device for the catch thread 
device, so that identical components of the said thread-cutting device 90 
are designated by the corresponding reference numerals of the said 
thread-cutting device 22. 
The said thread-cutting device 90 differs from the said thread-cutting 
device 22 in that no thread clamp and no locking member that can be 
introduced into the path of movement of the said hinge 47 of the said 
angle lever 29 are provided. Furthermore, a cutting knife 91, which is 
attached to the said needle plate 14, and whose cutting edge 92 is located 
at a shorter distance from the said stitch hole 51 than is the said 
cutting edge 43 in the first exemplary embodiment, is provided, instead of 
the cutting knife attached to a projection of the said base plate 2. The 
shorter distance between the point of cutting of the said thread-cutting 
device 90 and the said stitch hole 51 leads to a correspondingly elongated 
design of the said catch thread device 23. The front area of the said 
catch thread device 23, i.e., the area extending from the said barb to the 
said separating tip may have the same design as in the said catch thread 
device 23 according to the first exemplary embodiment. 
Mode of Operation 
Due to the use of the said pneumatic cylinder 34, to which pressure can be 
admitted at any time, for driving the said catch thread device 23, the 
mode of operation of the third exemplary embodiment is identical to the 
mode of operation of the first exemplary embodiment to the extent that the 
said catch thread device 23 is pivoted into the thread-catching position 
for shortening the needle thread end at the beginning of sewing at a time 
at which the end section of the said thread guide plate 18 is still in the 
area of the said stitch hole 51 in this case as well, and the two legs NN 
and NV of the needle thread loop are in contact, next to each other, with 
the said thread guide plate 18, as shown in FIGS. 8 and 9. 
During the further course of the first stitch formation cycle, the said 
hook 15 pulls the end of the needle thread under the said needle plate 14, 
as in the first exemplary embodiment, after which the thread loop is 
untied, and only the section of the needle thread that previously formed 
the reserve-side loop leg NV is subsequently in contact with the said 
catch thread device 23. 
The sewing machine is briefly stopped at the dead center of the said 
take-up lever 5 during this first stitch formation cycle, and the said 
pneumatic cylinder 34 is reversed. As a result, the said catch thread 
device 23 is returned into its starting position, and it carries the 
needle thread end NE. In contrast to the first exemplary embodiment, the 
said catch thread device 23 is completely returned into the starting 
position without interruption in the present, third exemplary embodiment, 
and part of the needle thread end NE is cut off. Due to the particularly 
short distance between the said cutting edge 92 and the said stitch hole 
51, a particularly short needle thread end is thus obtained on the fabric 
being sewn. 
After the first stitch formation process, the fabric being sewn is fed by 
the said feed dog 21 of the sewing machine to the extent that the section 
of the needle thread located within the fabric will come under the said 
pressure foot 7, and is held between this and the said needle plate 14 in 
a frictionally engaged manner. The holding force now acting on the needle 
thread end is sufficient to guarantee that the needle thread loop will be 
formed completely and led around the bobbin case during the next stitch 
formation cycle, so that satisfactory connection of the needle thread to 
the hook thread takes place. 
Exemplary Embodiment 4 
The design of the sewing machine shown in FIG. 13 is identical to that of 
the sewing machine according to the first exemplary embodiment, so that 
identical components are designated by the same reference numerals. 
A thread-cutting device 100, which essentially corresponds to the said 
thread-cutting device 22 according to the first exemplary embodiment, is 
arranged under the said base plate 2. To illustrate this fact, the 
components of the said thread-cutting device 100 in the fourth exemplary 
embodiment, which are identical to those according to the first 
embodiment, are provided with the same reference numerals. Thus, the said 
thread-cutting device 100 has a catch thread device 101, which is arranged 
coaxially to the said hook 15, and is in its starting position in FIG. 14. 
The said catch thread device 101 is attached to a said arm 24 of a said 
sleeve 25, which is rotatably mounted on a said bearing bush 26 of the 
said hook drive shaft 11. A said connecting rod 27 is hinged to the said 
arm 24, and the said connecting rod 27 is connected to a said 
longitudinally adjustable arm 28 of a said angle lever 29, which is 
carried by a said bearing block 30 that is an integral part of the 
housing. The said other arm 31 of the said angle lever 29 is connected via 
a said connecting rod 32 to the said piston rod 33 of a said pneumatic 
cylinder 34. The design and the control circuit of the said pneumatic 
cylinder 34 correspond to the pneumatic cylinder and the pneumatic 
cylinder control circuit for a thread-cutting device, which are disclosed 
in DE 32,44,996 C2. 
The said catch thread device 101 has a separating tip 102 designed at its 
free end (FIG. 16), and a thread-catching barb 103, which is directed in 
the opposite direction, is formed by an incision 104, and represents a 
first catching element. A fiat groove 105, which opens into a continuous 
elongated hole 106, is designed at the foot of the said barb 103. The edge 
107 of the said elongated hole 106 adjacent to the said separating tip 102 
is designed as a sharp edge, and is used as a cutter. 
A continuous hole 108, whose limiting surface 109 forms a second catching 
element, is provided in the said catch thread device 101 at a laterally 
spaced location from the said incision 104. The said hole 108 is connected 
to the said elongated hole 106 via a flat groove 110. The front section of 
the said catch thread device 101 between the said separating tip 102 and 
the said edge 107 is designated by 111. 
A cutting knife 112, whose cutting edge 113 is located at a relatively 
short distance from the said stitch hole 51 of the said needle plate 14, 
is fastened to the underside of the said needle plate 14. 
Mode of Operation 
The mode of operation of the said thread-cutting device 100 during thread 
cutting at the end of the sewing process is the same as that of the 
thread-cutting device according to DE 32,44,996 C2, so that this function 
does not need to be explained in greater detail. It should only be pointed 
out that the said catch thread device 101 is moved here from its starting 
position into the thread-catching position only when the said thread guide 
plate 18 has already withdrawn from the two legs NN and NV of the needle 
thread loop, or the legs NN and NV have fallen off from the said thread 
guide plate 18. This point in time is of significance because, in the case 
of a double rotary hook doubly rotating around a horizontal axis, the 
fabric-side loop leg NN is moved past the front side of the said bobbin 
case 20, and the reserve-side loop leg NV is moved past the rear side of 
the said bobbin case holder 19, so that the two legs NN and NV extend, 
after falling off from the said thread guide plate 18, at different angles 
in relation to the said stitch hole 51 of the said needle plate 14. In 
this thread course, the said catch thread device 101 with its said 
separating tip 102 can be reliably moved between the two loop legs NN and 
NV, and the fabric-side loop leg NN is caught by the said barb 103 and fed 
to the said cutting knife 113 during the return movement of the said catch 
thread device 101, and the reserve-side loop leg NV is kept away from the 
said cutting knife 113. The cutting off of the fabric-side loop leg NN 
leads, as desired, to a short needle thread end on the fabric in the area 
of the end of the seam, on the one hand, and, on the other hand, a long 
reserve-side needle thread end, which is necessary for the reliable 
connection of the needle thread end to the hook thread at the beginning of 
the next sewing process, is obtained. The common term "needle thread end," 
which is designated by the reference NE, is defined here as the thread 
section extending from the said needle 4 to the actual end E of the needle 
thread. 
Pressure is admitted to the said pneumatic cylinder 34 prior to the 
beginning of the first stitch formation cycle, as a consequence of which 
the said catch thread device 101 is moved from its starting position shown 
in FIGS. 13 and 14 into the thread-catching position shown in FIGS. 15 and 
20, in which the path of movement N of the said needle 4 passes through 
the center of the said hole 108. 
At the beginning of the first stitch formation cycle carried out 
subsequently at reduced speed, the said needle 4 pulls a section of the 
loose needle thread end NE through the said stitch hole 51 and the said 
hole 108 of the said catch thread device 101 in the downward direction (it 
is achieved due to the said thread wiper 8 that the needle thread end NE 
will not come under the said pressure foot 7 and will not be held by 
same), after which the needle thread end NE is caught by the said hook tip 
17 and is moved as a thread loop around the bobbin housing formed by the 
said bobbin case holder 19 and the said bobbin case 20. As was mentioned, 
the reserve-side loop leg NV now extends behind the said bobbin case 
holder 19, while the other loop leg, which leads to the end E of the 
needle thread, extends on the front side of the said bobbin case 20. This 
loop leg is comparable to the loop leg that forms the fabric-side loop leg 
NN after the first stitch formation. The loop leg leading to the actual 
end E is therefore also designated by NN. 
In the course of leading the needle thread loop around the bobbin housing, 
the end E of the needle thread is pulled under the said needle plate 14, 
after which the thread loop is untied, and the needle thread end NE will 
subsequently hang down freely from the said hole 108 of the said catch 
thread device 101. However, it is now guaranteed that the needle thread 
end NE always passes through the said hole 108, and is consequently caught 
by the said catch thread device 101, completely regardless of how and 
where the rest of the needle thread end NE extends. 
The sewing machine is briefly stopped at the top dead center of the said 
take-up lever 5 during this first stitch formation cycle, and the said 
pneumatic cylinder 34 is reversed. As a result, the said catch thread 
device 101 is returned into its starting position, carrying the needle 
thread end NE with it. In contrast to the first exemplary embodiment, the 
said catch thread device 101 is returned completely into the starting 
position without interruption in this fourth exemplary embodiment, and 
part of the needle thread end NE is cut off. A particularly short needle 
thread end is obtained on the fabric here because of the particularly 
short distance between the said cutting edge 114 and the said stitch hole 
51. 
After the first stitch formation process, the fabric is fed by the said 
feed dog 21 of the sewing machine to the extent that the section of the 
needle thread located in the fabric will come under the said pressure foot 
7 and be held between same and the said needle plate 14 in a frictionally 
engaged manner. The holding force now acting on the needle thread end is 
sufficient to guarantee the formation and complete leading of the needle 
thread loop around the bobbin housing during the next stitch formation 
cycle, so that satisfactory connection of the needle thread to the hook 
thread will take place. 
Instead of the said catch thread device 101 shown in FIG. 16, it is also 
possible to use a catch thread device 121 designed according to FIG. 17 in 
the fourth exemplary embodiment. The said catch thread device 121 is 
essentially identical to the said catch thread device 101. It also has a 
separating tip 122 and a barb 123, which is formed by an incision 124 and 
represents a first catching element. Furthermore, a flat groove 125, which 
opens into a continuous elongated hole 126, is designed at the foot of the 
said barb 123. The edge 127 of the said elongated hole 126 adjacent to the 
said separating tip 122 is designed as a sharp edge and is used as a 
cutting edge. 
A continuous hole 128, whose limiting surface 129 forms a second catching 
element, is provided in the said catch thread device 121 at a laterally 
spaced location from the said incision 124. The edge area 130 of the said 
hole 128, which faces the said separating tip 122 and is located on the 
top side of the said catch thread device 121, is designed as a sharp edge 
area, and is used as a cutting edge. The front section of the said catch 
thread device 121 between the said separating tip 122 and the said edge 
127 is designated by 131. The said cutting knife 113 is associated with 
the said catch thread device 121, just as with the said catch thread 
device 101, but the cutting process is brought about in this case by the 
cooperation of the said sharp-edged edge area 130 of the said catch thread 
device 121 and the said cutting edge 114 of the said cutting knife 113. 
The rest of the mode of operation in the case of the use of the said catch 
thread device 121 is the same as in the case of the said catch thread 
device 101, so that a more detailed description is unnecessary. 
Exemplary Embodiment 5 
In the fifth exemplary embodiment shown in FIG. 18, the design of the 
sewing machine, including the hook, is identical to that of the fourth 
embodiment, so that identical components are designated by the same 
reference numerals. This also applies to the thread-cutting device 
designated by 140, i.e., its design from the said catch thread device 101 
up to and including the said angle lever 29 is identical to that of the 
said thread-cutting device 100. 
The drive for the said catch thread device 101 is derived, in the same 
manner as in the second exemplary embodiment according to FIG. 5, from the 
said cam 61, which is attached to the said main shaft 13 and has a said 
control groove 62 and a said control segment 63. A said axially 
displaceable shaft 64 is arranged in parallel to the said main shaft 13. A 
said control lever 66, provided with a said roller pin 65, as well as a 
said release lever 67 are fastened to the said shaft 64. A said detent 
pawl 69 is mounted freely rotatably on a said bearing bush 68 of the said 
shaft 64. A said spring 70, which is wound around the said shaft 64, and 
which is in contact with the said control lever 66 at one end and with the 
said detent pawl 69 at the other end, causes the said detent pawl 69 to be 
pivoted in the direction of the said control segment 63 and the said 
roller pin 65 to be pivoted out of the said control groove 62. At the same 
time, the said spring 70 acts as a compression spring, and displaces the 
said shaft 64 into the right-hand end position shown in FIG. 18, in which 
the said roller pin 65 is located opposite the said control groove 62 when 
the needle of the sewing machine is in the deep position. A spring-loaded 
starting lever, not shown, which can be actuated by an electromagnet, 
likewise not shown, is located opposite the said release lever 67. 
A locking piece 71 is fastened to the side of the said control lever 66, 
which is in the right-hand end position. The said locking piece 71 is 
designed such that it forms an axially acting movement barrier for the 
said control lever 66 only when the said control lever 66 is in its 
resting position away frown the said cam 61, whereas the said control 
lever 66, pivoted into its operating position, is able to move under it. 
At the end of the shaft 64 facing the said hook 15, the said carrier piece 
72 is mounted rotatably, but in an axially fixed position. The said 
carrier piece 72 is connected to the said arm 31 of the said angle lever 
29 via a said telescoping connecting rod 73. The said telescoping 
connecting rod 73 has a bar 74, which is hinged at one end to the said 
angle lever 29, whose other end is provided with threads, and is screwed 
together with a said sleeve 75 of a corresponding design. A said 
piston-like stop piece 76, which is fastened to one end of a said bar 77 
passing through the bottom of the said sleeve 75, is accommodated in the 
said sleeve 75. The other end of the said bar 77 is hinged to the said 
carrier piece 72. A said transversely projecting pin 78, which passes 
through an elongated hole 79a in the said sleeve 75, is arranged in the 
said stop piece 76. The said elongated hole 79a is made considerably 
longer than the said corresponding elongated hole 79 in the second 
exemplary, embodiment according to FIG. 5. A said compression spring 80 
arranged in the said sleeve 75 holds the said stop piece 76 in the 
starting position shown in FIG. 18, in which the said pin 78 is in contact 
with the left-hand end of the said elongated hole 79a. 
An additional drive mechanism in the form of a stationarily arranged 
pneumatic cylinder 141, whose piston rod 142 carries a stop plate 143, is 
associated with the said thread-cutting device 140 [reference numeral 140 
designates an edge area in Exemplary Embodiment 4--Tr. Ed.]. When pressure 
is admitted to the pneumatic cylinder 141, the stop plate 143 strikes the 
said hinge 47 of the said angle lever 29, and pivots the said catch thread 
device 101 into the catching position shown in FIGS. 15 and 20. 
Mode of Operation 
Since the said catch thread device 101 in the exemplary embodiment 
according to FIG. 18 must be moved for shortening the needle thread end at 
the beginning of sewing in a hook position different from that during 
thread cutting at the end of the seam, but it cannot be driven by the said 
cam 61 in the manner necessary because of the permanent association of the 
said cam 61 with the said main shaft 13, the said catch thread device 101 
is moved by means of the said pneumatic cylinder 141, prior to the 
beginning of the first stitch formation cycle, into its catching position, 
in which the path of movement N of the said needle 4 passes through the 
center of the said hole 108. 
Since the said control lever 66 is in the resting position away from the 
said cam 61 during the forward movement of the said catch thread device 
101 into the thread-catching position, in which position the said locking 
piece 71 forms an axially acting movement barrier for the said control 
lever 66 and the said shaft 64 carrying same, a relative movement 
correspondingly takes place between the said sleeve 74 driven by the said 
angle lever 29 and the said fixed stop piece 76 accommodated in the said 
sleeve 74, and the said compression spring 80 is compressed. 
At the beginning of the first stitch formation cycle performed subsequently 
at reduced speed, the said needle 4 pulls part of the loose needle thread 
end NE through the said stitch hole 51 and into the said hole 108 of the 
said catch thread device 101, after which the needle thread end NE is 
caught by the said hook tip 17, and is completely pulled under the said 
needle plate 14, while the needle thread end NE, which is now hanging down 
freely, passes through the said hole 108. 
The sewing machine is briefly stopped at the top dead enter of the said 
take-up lever 5 during this first stitch formation cycle, and the said 
pneumatic cylinder 141 is reversed. The said compression spring 80, which 
is now being released, subsequently pulls the said catch thread device 101 
into the starting position shown in FIG. 18 via the said sleeve 74 and the 
said angle lever 29, and part of the needle thread end NE is cut off due 
to cooperation of the said edge 107 of the said catch thread device 101 
with the said cutting edge 114 of the said cutting knife 113. 
The fabric being sewn is fed by the said feed dog 21 after the first stitch 
formation cycle to the extent that the section of the needle thread 
located within the fabric being sewn will come under the said pressure 
foot 7 and will be held between this [the pressure foot] and the said 
needle plate 14 in a frictionally engaged manner. As a result, it is 
guaranteed that a complete needle thread loop can be formed during the 
next stitch formation cycle, as a consequence of which satisfactory 
connection of the needle thread to the hook thread can take place. 
Exemplary Embodiment 6 
In the sixth exemplary embodiment shown in FIG. 19, the design of the 
sewing machine, including the hook, is identical to that of the fifth 
exemplary embodiment according to FIG. 18, so that identical components 
are designated by the same reference numerals. This also applies to the 
thread-cutting device designated by 150, i.e., its said catch thread 
device 101 is in connection with the same drive mechanism as in the fifth 
exemplary embodiment. Since the corresponding components are identical, 
FIG. 19 shows only the said arm 28 of the said angle lever 29, and the 
rest of the drive mechanism is omitted. 
A cutting knife 151, which is represented by dash-dotted lines in FIG. 19, 
and which is designed and arranged in the same manner as the said cutting 
knife 42 of the first exemplary embodiment shown in FIG. 2, is associated 
with the said catch thread device 101. A leaf spring 152, which is also 
represented by dash-dotted lines only, and forms a thread clamp 153 
together with the said incision 111 of the said catch thread device 101, 
is fastened above the said cutting knife 151. 
A one-armed lever 155 is provided on a stationarily mounted pin 154 under 
the said angle lever 29. A first pneumatic cylinder 156, which has a stop 
plate 158 fastened to the piston rod 157, is associated with the said 
lever 155. The said lever 155, whose free end is in contact with the said 
stop plate 158, extends essentially horizontally when the said piston rod 
157 is withdrawn. The said pneumatic cylinder 156 is located essentially 
under the said hinge 47 of the said angle lever 29. A second pneumatic 
cylinder 159 of equal size, whose piston rod 160 carries a stop plate 161, 
is stationarily arranged at a laterally spaced location from the said 
first pneumatic cylinder 156. The contact point between the said stop 
plate 161 and the said lever 155 is located between the said pin 154 and 
the said contact point between the said stop plate 158 and the said lever 
155. The said two pneumatic cylinders 156 and 159 form together an 
additional drive mechanism for the said thread-cutting device 150. 
Mode of Operation 
Prior to the beginning of the first stitch formation cycle, the said catch 
thread device 101 is moved by means of the said pneumatic cylinder 159 and 
of the said lever 155 acting on the said hinge 47 into its catching 
position, in which the path of movement N of the said needle 4 passes 
through the center of the said hole 108. The said compression spring 80 of 
the said telescoping connecting rod 73 is compressed during the forward 
movement of the said catch thread device 101 into the catching position in 
the same manner as in the fifth exemplary embodiment. 
At the beginning of the first stitch formation cycle performed subsequently 
at reduced speed, the said needle 4 pubs part of the loose needle thread 
end NE through the said stitch hole 51 and the said hole 108 of the said 
catch thread device 101, after which the needle thread end NE is caught by 
the said hook tip 17 and is completely pulled under the said needle plate 
14, and the needle thread end NE, which is now hanging down freely, passes 
through the said hole 108. 
After the said catch thread device 101 has reached its thread-catching 
position, pressure is admitted to the said pneumatic cylinder 156, and the 
said stop plate 158 is moved into the top position, in which it is still 
located at a spaced location from the free end of the said lever 155, 
which is pivoted upward by means of the said other pneumatic cylinder 159. 
The sewing machine is briefly stopped at the top dead enter of the said 
take-up lever 5 during this first stitch formation cycle, and the said 
pneumatic cylinder 159 is reversed. The said compression spring 80, which 
is being released, subsequently withdraws the said catch thread device 101 
in the direction of its starting position, and the said catch thread 
device 101 carries the needle thread end NE passing through the said hole 
108, and pubs it under the said leaf spring 152, as in the first exemplary 
embodiment. 
The said stop plate 158 of the said pneumatic cylinder 156, which is in the 
raised position, causes the said catch thread device 101 not to be able to 
be completely withdrawn into its starting position at this point in time, 
but to stop in the position corresponding to FIG. 12, in which position 
its front section 111 is located under the end piece of the said leaf 
spring 152, forms the said thread clamp 153 together with it [the said 
leaf spring 152], and the said edge 107 is still located at a spaced 
location in front of the cutting edge of the said cutting knife 151. In 
this position of the said catch thread device 101, the needle thread end 
NE arriving from the said stitch hole 51 extends between the end of the 
said leaf spring 152 and the said front section 111 of the said catch 
thread device 101, and is clamped between them. The needle thread end NE 
extends from this point of clamping under the cutting edge of the said 
cutting knife 151, beyond the said elongated hole 106, through the said 
groove 110 and the said hole 108, to hang freely down from this [the said 
hole 108]. 
After the needle thread end NE has been introduced into the said thread 
clamp 153, the sewing machine performs the second stitch formation cycle. 
Since the needle thread end NE is now held, the said hook 15 is able to 
completely loop the needle thread around the bobbin housing, and to catch 
the free end of the hook thread G. The needle thread loop is then 
withdrawn by the subsequent upward movement of the said take-up lever 5, 
and the first thread connection of the needle thread with the hook thread 
is tightened. 
The sewing machine is again stopped briefly at the top dead center of the 
said take-up lever 5 during the second stitch formation cycle, and the 
said pneumatic cylinder 156 is subsequently reversed, and the said stop 
plate 158 is returned into its lower position. The said compression spring 
80, which is being increasingly released, subsequently causes the said 
catch thread device 101 to be returned into the starting position, and 
part of the needle thread end NE is cut off.