Title of Invention	METHOD OF PULLING THE FREE END OF A NEEDLE THREAD FROM THE TOP TO THE BOTTOM SIDE OF A WORK PIECE AND SEWING MACHINE FOR PUTTING THE METHOD INTO PRACTICE
Abstract	In a method of pulling the free end (83) of the needle thread (62) from the top of the bottom of at least one work piece (74, 75) upon a first stitch of a seam (81) that is to be sewn, use is made of a sewing machine with at least one presser (25) which can be placed on, and lifted off, the work piece (74, 75). The needle thread (62) is held tight while a needle-thread loop (78) is extended by the tip of the hook (13) so that the free end (83) is pulled through the work piece (74, 75). While the needle thread (62) is held tight, the presser (25) is at least partially relieved. The relief time increases as the thickness (s) of the work piece (74, 75) grows.

Title of Invention

METHOD OF PULLING THE FREE END OF A NEEDLE THREAD FROM THE TOP TO THE BOTTOM SIDE OF A WORK PIECE AND SEWING MACHINE FOR PUTTING THE METHOD INTO PRACTICE

Abstract

In a method of pulling the free end (83) of the needle thread (62) from the top of the bottom of at least one work piece (74, 75) upon a first stitch of a seam (81) that is to be sewn, use is made of a sewing machine with at least one presser (25) which can be placed on, and lifted off, the work piece (74, 75). The needle thread (62) is held tight while a needle-thread loop (78) is extended by the tip of the hook (13) so that the free end (83) is pulled through the work piece (74, 75). While the needle thread (62) is held tight, the presser (25) is at least partially relieved. The relief time increases as the thickness (s) of the work piece (74, 75) grows.

Full Text	The invention relates to a method of pulling the free end of a needle thread from the top to the bottom side of at least one work piece upon a first stitch of a seam to be sewn by a sewing machine comprising, a needle which is movable in upward down reciprocation guiding a needle thread that has been taken from a needle - thread supply by a thread leaves and at least one presser to be place on and lifted off and a ratarity drivable look a tip which a needle thread loop and entents it for forming a stitch and with the needle thread being held tight between the needle and the thread lever while the needle - thread loop is extend so that a free end is pulled through the work piece by the hook tip and with the presser being at least partially relieved while the needle thread is held tight and to a sewing machine for putting the method into practice comprising a needle which is movable is up and down reciprocation, guiding a needle thread that has been taken from a needle - thread supply by a thread lever one presser to be placed on and lifted off, the at least one work piece and a ratarily drivable hook, the tip of which seizes a needle thread loop and extends if for forming a stitch and a needle - thread clamp which is stationarily provided between the thread lever and the needle and a presser drive and a control system for the thread clamp and the press drive. In a method of the generic type, the object is attained by the feature of the work piece increases in thickness, the relief time rises. The measures according to the invention ensure that the duration of relief rises as the thickness of a work piece increases. Preferably, this is done indirectly by the relief time, depends on the length of the stroke of the at least one presser input of the length stroke in adaptation to the sewing job being possible on the side of the machine. According to the invention, the object is attained by the feature of a presser - relief drive is triggered by the controller system in accordance with a function which is recorded in the control system, reflecting the dependency of the time of actuation of the presser-relief drive on the thickness of the at least one work piece in a sewing machine. Details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing, in which Fig. 1 is a elevation of a sewing machine; Fig. 2 is an illustration, on an enlarged scale, of a thread clamp of the sewing machine; Fig. 3 is a diagrammatic side view, on an enlarged scale, of the sewing machine in accordance with the arrow III of Fig. 1; Fig. 4 is a perspective diagrammatic view of the stitch-form ing area of the sewing machine; Fig. 5 is an illustration of the needle of the sewing machine in downward motion upon production of a first stitch in the work pieces; Fig. 6 is an illustration of two work pieces assembled by a seam with the tail pieces of needle and hook threads on the bottom side of the work pieces; and Fig. 7 is a path-time diagram plotting the time of operation of a presser relief drive over the length of stroke of the presser. INVENTION As shown in fig 1, the sewing machine seen in the drawing machine seen in the drawing comprises a top arm 1 and a bottom base plate 2 in the form of a casing, the two being assembled by a standard 3 to form a C-shaped casing. An arm shaft 4 is mounted in the arm 1, drivable via a belt drive 5 by a motor 6. A control box 7 is joined to the motor 6, housing a microprocessor control system 8. A needle bar 10 is driven in up and down reciprocation by the arm shaft 4 by means of a crank 9 (fig. 3 right side, 5th item from top) a needle 11 is fixed to the lower end of the needle bar 10. A hook 12 is disposed in the base plate 2, which is conventionally driven in rotation about its axis, derived from the arm shaft 4. The hook 12 is provided with a thread supply 13. A lifting mechanism 14 (fig. 1,3) disposed in the arm 1, serving for setting the length of stroke a of work-piece pressers (described below); a setting shaft 15 forms art of it. The setting shaft 15 (fig. 1,3) has a guiding groove 16 (fig 3) with a crosshead 17 (fig. 3) longitudinally displaceable therein. An end of a lever 18 (fig. 3) is pivotably mounted on the crosshead 17 (fig. 3); the other end is articulated to a first arm 19 (fig. 3) of an elbow lever 20 (fig. 3). The elbow lever 20 is pivotably supported on a bearing 22 (fig. 3) stationary on the machine, at the point of intersection of its first arm 19 and its second arm 21. A tie rod 23 (fig. 3), which engages with a cam 24 (fig. 3), acts approximately centrally on the lever 18 (fig. 3); the cam 24 (fig. 3) is coupled with the arm shaft 4 (fig. 1,3). The arm 1 (fig. 1,13) is provided with a presser 25 (fig 4,5, 3) which has a presser bar 27 (fig. 3) that is vertically displaceable in as sliding bearing 26 (fig. 3) and a presser foot 28 (3,4,5) at the bottom end of the presser bar 27 (fig. 3). By the side of the presser 25, provision is made for a feeder 29 (fig. 3,4,5), equally having the function of a presser and including a feed bar 31 (fig. 3) which is displaceable in a sliding bearing 30 (fig. 3) and to the bottom end of which is fixed a feeder foot 32 (fig. 3,5). The sliding bearing 30 (fig. 3), and thus the feeder 29 (fig. 3), are mounted on a swing frame 33 (fig. 3) where also the needle bar 10 is lodged for displacement in another sliding bearing 34 ( fig. 3) the feeder bar 31 (fig. 3) and the needle bar 10 (fig. 3) being paralled to one another. The swing frame 33 (fig. 3) is pivotably mounted on a bearing 35 (fig. 3) in the arm 1 (fig. 1,3), driven by a sliding gear transmission via a tie rod 36 (fig. 3) that is pivotably joined to the swing frame 33 via a bearing 37 (fig. 3). A sliding gear transmission of this type is known from DE34 23 843 C2 (corresponding to U.S. patent 4 616 586). Actuation of the presser 25 (fig. 3.4.5) and feeder 29 (fig. 4,5) take place from the elbow lever 20 (fig. 3), the second arm 21 (fig. 3) of which is articulated toa traingualr driving lever 38(fig. 3), the second arm 21 being joined to a tip of the driving lever 38 (fig. 3) by way of a tie rod 21a (fig. 3). Transmission levers 39, 40 are articulated to the two other tips; they are articulated to the upper ends of the presser bar 27 (fig. 3) and the feeder bar 31 (fig. 3), respectively. The driving lever 38 pivotably supports itself via a rod 41 (fig. 3) on a bearing 42 (fig. 3) which disposed in the arm 1 (fig. 1,3). The rod 41 (fig. 3) is loaded by a pre-stressed helical compression spring 43 (fig. 3) so that the rod 41 (fig. 3) and thus the presser 25 (fig. 3) the feeder 29 (fig. 3) are forced downwards. Disposed underneath the rod 41 (fig. 3) is a stop lever 44 (fig. 3) which is also pivotable in the bearing 42 (fig. 3) , having a stop 45 that is allocated to the rod 41 underneath the compression spring 43 (fig. 3). A stop setting drive 46 in the form of a pneumatically actuated piston cylinder drive acts on the stop lever 44 (fig. 3), its piston rod 47 (fig. 3) being articulated to the stop lever 44 (fig. 3) while its cylinder 48 (fig. 3) is joined to the standard 3(fig. 3) . the drive 46 (fig. 3) is a unilaterally actuated piston cylinder drive i.e., a piston 49 (fig. 3) is mounted on the piston rod 47 (fig. 3), with compressed air being admitted via a compressed-air piping 50 (fig. 3) to the side of the piston 49 that faces away from the piston rod 47 (fig, 3) so that upon admission of compressed air the piston rod 47 (fig. 3) is pushed out of the cylinder 48 (fig. 3), whereby the stop 45 (fig. 3) is adjusted towards the stop lever 44 (fig. 3). Upon pressure relief, the piston 49 (fig. 3) and thus the piston rod 47 (fig. 3) are restored by means of a readjusting spring 51 (fig. 3). Actuation by compressed air is controlled by a 3/2-port directional control valve 52 (fig. 3) to which compressed air is supplied from a source of compressed air (not shown) via compressed-air supply piping 53 (fig. 3). On the other hand it is operated electromagneticlly, to which end it is connected to the control system 8 (fig. 3) via an electric line 54 (fig. 3 The setting shaft 15 (fig. 3) for the presser 25 (fig. 3) is provided with a working lever 55 (fig. 3), by means of which to pivot the setting shaft 15 (fig. 3) about its axis, changing the position of the corsshead-17 guiding groove 16 (fig. 3). The working lever 55 (fig. 3) serves to fix the length of stroke a of the presser 25 (fig. 3) and the feeder 29. The smallest and greatest adjustable length of stroke a is defined by two adjustable limit stops 56, 57 (fig. 3) which are which are mounted on the arm 1 (fig. 1,3) and between which acts a lever 58 that is mounted on the setting shaft 15 (fig. 3) . For example, 2.0 mm ≤ a ≤ 8.0 mm applies. A rotary potentiometer 59 (fig. 3) is coupled with the setting shaft 15, visa a signal line 60 signalling, to the control system 8 (fig. 3), the position of angle rotation of the setting shaft 15 (fig. 3) as a measured variable. The arm 1 (fig. 1,3) includes a needle-thread supply 61 (fig. 3), which is illustrated only in Fig. 4. From this supply61 (fig. 3), the needle thread 62 (fig. 3) is conventionally led via a thread tightener 63 (fig. 3), a thread lever 64 and a thread clamp 65 (fig. 3) to the needle 11 (fig. 3). The thread tightener 63 (fig. 3) is described in DE 28 09 848 C2 (corresponding to U.S. patent 4 289 087). It comprises two tension disks 68, with the needle thread 62 passing there -between, and a solenoid 67. Corresponding to the voltage fed to the solenoid 67 (fig. 3), adjustable frictional force is exercised on the needle thread 62 (fig. 3) between the tension disks 66 (fig. 3), conferring a corresponding tension to the thread. The thread clamp 65 (fig. 3), which is directly upstream of the needle 11 (fig. 3), comprises a tension disk 68 (fig. 3) fixed to a guide bar 69 (fig. 3) that is again loaded by a compression spring 70 (fig. 3), whereby the tension disk 68 (fig. 3) is forced against an abutment 71 (fig. 3) that is fastened to the arm 1 (fig. 3). Provided on the abutment 71 (fig. 3) is a solenoid 71 (fig. 3) formed by wire winding 72 (fig. 3) which can be triggered via a line 73 (fig. 3) from the control system 8 (fig. 3). For a sewing job, two work pieces 74, 75 are passed one on top of the other on to the needle plate 76 (fig. 3) that is provided on the base plate 2 (fig. 3). The needle plate 76 (fig. 3) has a recess which a bottom feeder 77 (fig. 3) projects through, having a stitch hole 77 (fig. 3) a for the needle 11 to pass through. The bottom feeder 77 (fig. 3) is kinematically linked to the mentioned sliding gear transmission such that the stitch hole 77 (fig. 3) a is moved synchronously with the needle 11 (fig. 3) stitching into the work pieces 74, 75 (fig. 3) during stitch formatiion and equally performing the feed motion. The described design and mode of operation are familiar general practice in so-called needle-feed sewing machines. The two work pieces 74, 75 have a total thickness s. The length a by which the feet 28, 32 are lifted above the work pieces 74, 75 is set by an operator by means of the working lever 55. Assumably the operator increases the length of stroke a as the thickness s of the work pieces 74, 75 grows, the compressibility of the two work pieces 74, 75 increasing as the thickness s increases. In a standard sewing operation, the needle 11, together with the needle thread 62, passes through the work pieces 74, 75 into the stitch hole 77a. The feeder foot 32 is in a lowered and the feeder 77 in an elevated position so that the work pieces 74, 75 are clamped between the feeder 77 and the feeder foot 32. At this time the presser foot 28 is above the work piece 74 corresponding to the length of stroke a so that unimpeded feed of the work pieces 74, 75, with the needle 11 passed there-through, is possible in the direction of feed 82. The thread clamp 65 is opened so that the needle thread 62 can be supplied unimpeded by the downward motion of the nee- dle 11. When the needle 11, after passing through its lowermost position, has again moved upwards by approximately 2.5 mm, the tip 79 of the rotating hook 12 seizes the needle-thread loop 78 formed upon upward motion of the needle 11. With the upward motion proceeding, the needle 11 finally re- tracts from the work pieces 74, 75. Meanwhile the hook 12 has caused the needle thread loop 78 to entirely surround the hook-thread supply 13. Then the excess needle thread 62 is retracted by the thread lever 64 with a two- thread lock-stitch seam 81 forming. Afterwards the presser foot 28 and the feeder foot 32 are shifted so that the presser foot 28 is placed on the work pieces 74, 75 and the feeder foot 32 is lifted off by the length of stroke a. During a standard sewing operation, the thread clamp 65 only serves as a guide of the needle thread 62, not braking it. The described way of stitch forming and the mode of alternating operation of the feet 28, 32 with nee- dle feed are familiar and general practice. When a first stitch of a seam 81 is to be sewn, the free end 83 of the needle thread 62 i.e., the needle-thread starting end, is above the work pieces 74, 75; it is clamped between the upper work piece 75 and the presser foot 28 by a force that depends on the pre-load of the compression spring 43. For this free end 83 to be pulled downwards through the work pieces 74, 75 when the needle-thread loop 78 is extended upon corresponding revolution of the hook tip 79, the presser foot 28 must be relieved while the needle- thread loop 78 is extended. This is effected by corresponding actuation of the stop setting drive 46 by compressed air, whereby the stop lever 44 and the stop 45 are elevated, bearing against the rod 41. In doing so, the trian- gular driving lever 38 is slightly pivoted, as a result of which the presser bar 27 and thus the presser foot 28 are slightly lifted without the presser foot 28 being removed from the work pieces 74, 75, which implies pressure relief of the work pieces 74, 75 and, consequently, reduction of the fric- tional force that impedes the free end 83 of the needle thread 62 in being pulled out. The accompanying downward motion of the feeder foot 32 is of no importance functionally, the foot 32 not coming in touch with the work pieces 74, 75. As can be seen from the above, the stop setting drive 46 is a presser-25-relief drive. Relieving the feeder foot 32 for the free end 83 of the needle thread 62 to be pulled to the bottom side of the work piece 75 is in principle known from DE 36 04 299 C2 (corresponding to U.S. 4 658 752). The distance b of the stop 45 from the rod 41 grows as the thickness s of the work pieces 74, 75 increases i.e., the idle stroke from when the piston rod 47 starts extending to the moment when the stop 45 bears against the rod 41, increases as work-piece thickness s increases. For this to be com- pensated, the time of activation of the stop setting drive 46 is increased as the length of stroke a increases, which takes place in accordance with an empirically determined function roughly outlined in Fig. 7, where the ac- tuation time t is plotted above the length of stroke a. This function is re- corded in a ROM 84 of the control system 8. The length of stroke a is passed to the control system 8 by the rotary potentiometer 59 upon corre- sponding adjustment of the setting shaft 15, there setting off the valve 52, and thus the drive 46, to be triggered in accordance with the function t = f (a). The greater the work piece thickness s, the greater is the length of stroke a - as outlined above. Any increase in length of stroke a is accom- panied with an increase in the duration of triggering of the stop setting drive 46, which compensates the time loss during idle stroke over the length b. Moreover the compressibility of the work pieces 74, 75, which increases as the thickness s of the work pieces 74, 75 grows, is balanced. WE CLAIM 1. A method of pulling a free end (83) of a needle thread (62) from a top of a bottom side of at least one work piece (74, 75) upon a first stitch of a seam (81) that is to be sewn by a sewing machine, comprising - a needle (11) which is movable in up and down reciprocation, guiding a needle thread (62) that has been taken from a needle-thread supply (61) by a thread lever (64); - at least one presser (25) to be placed on, and lifted off, the at lease one work piece (74, 75); and - a rotarily drivable hook (12), a tip (79) of which seizes a needle-thread loop (78) and extends it for forming a stitch, - with the needle thread (62) being held tight between the needle (11) and the thread lever (64) while the needle-thread loop (78) is - extended so that a free end (83) is pulled through the work piece (74, 75) by the hook tip (79), and - with the presser (25) being at least partially relieved while the needle thread (62) is held tight; wherein as the at least one work piece (74, 75) increases in thickness (s), the relief time (t) rises. 2. A method as claimed in claim 1, wherein relief takes place in dependence on the length of stroke (a) of the at least one presser (25). 3. A sewing machine for putting into practice the method as claimed in one of claims 1 or 2, comprising - a needle (11) which is movable in up and down reciprocation, guiding a needle thread (62) that has been taken from a needle-thread supply (61) by a thread lever (64); - at least one presser (25) to be placed on, the lifted off, the at least one work piece (74, 75); and - a rotarily drivable hook (12), the tip (79) of which seizes a needle-thread loop (78) and extends it for forming a stitch, - a needle-thread-(62) clamp (65) which is stationarily provided between the thread lever (64) and the needle (11). - a presser drive; and - a control system (8) for the thread clam (65) and the presser drive; wherein a presser-relief drive is triggered by the control system (8) in accordance with a function which is recorded in the control system (8), reflecting the dependency of the time of actuation of the presser-relief drive on the thickness (s) of the at least one work piece (74, 75). 4. A sewing machine as claimed in claim 3, wherein a feeder (29) is provided, which is drivable alternately of the presser (25); a joint drive is provided for the presser (25) and the feeder (29); and the presser-relief drive is a presser-lift - off drive (46). 5. A sewing machine as claimed in claim 4, wherein an adjustable lifting mechanism (14) is provided for adjustment of the length of stroke (a) of the presser (25); and a potentiometer (59), which is coupled with the lifting mechanism (14), is provided for detection and transmission, to the control system (8), of a measured variable representing the length of stroke (a) of the presser (25) which is adjusted on the lifting mechanism (14). In a method of pulling the free end (83) of the needle thread (62) from the top of the bottom of at least one work piece (74, 75) upon a first stitch of a seam (81) that is to be sewn, use is made of a sewing machine with at least one presser (25) which can be placed on, and lifted off, the work piece (74, 75). The needle thread (62) is held tight while a needle-thread loop (78) is extended by the tip of the hook (13) so that the free end (83) is pulled through the work piece (74, 75). While the needle thread (62) is held tight, the presser (25) is at least partially relieved. The relief time increases as the thickness (s) of the work piece (74, 75) grows.

Full Text

The invention relates to a method of pulling the free end of a needle thread from
the top to the bottom side of at least one work piece upon a first stitch of a seam to
be sewn by a sewing machine comprising, a needle which is movable in upward
down reciprocation guiding a needle thread that has been taken from a needle -
thread supply by a thread leaves and at least one presser to be place on and lifted
off and a ratarity drivable look a tip which a needle thread loop and entents it for
forming a stitch and with the needle thread being held tight between the needle and
the thread lever while the needle - thread loop is extend so that a free end is pulled
through the work piece by the hook tip and with the presser being at least partially
relieved while the needle thread is held tight and to a sewing machine for putting
the method into practice comprising a needle which is movable is up and down
reciprocation, guiding a needle thread that has been taken from a needle - thread
supply by a thread lever one presser to be placed on and lifted off, the at least one
work piece and a ratarily drivable hook, the tip of which seizes a needle thread loop
and extends if for forming a stitch and a needle - thread clamp which is stationarily
provided between the thread lever and the needle and a presser drive and a control
system for the thread clamp and the press drive.
In a method of the generic type, the object is attained by the feature of the work
piece increases in thickness, the relief time rises. The measures according to the
invention ensure that the duration of relief rises as the thickness of a work piece
increases. Preferably, this is done indirectly by the relief time, depends on the
length of the stroke of the at least one presser input of the length stroke in
adaptation to the sewing job being possible on the side of the machine.

According to the invention, the object is attained by the feature of a presser - relief
drive is triggered by the controller system in accordance with a function which is
recorded in the control system, reflecting the dependency of the time of actuation of
the presser-relief drive on the thickness of the at least one work piece in a sewing
machine.
Details of the invention will become apparent from the ensuing description of an
exemplary embodiment, taken in conjunction with the drawing, in which
Fig. 1 is a elevation of a sewing machine;
Fig. 2 is an illustration, on an enlarged scale, of a thread clamp of the sewing
machine;
Fig. 3 is a diagrammatic side view, on an enlarged scale, of the sewing machine in
accordance with the arrow III of Fig. 1;
Fig. 4 is a perspective diagrammatic view of the stitch-form ing area of the sewing
machine;
Fig. 5 is an illustration of the needle of the sewing machine in downward motion
upon production of a first stitch in the work pieces;
Fig. 6 is an illustration of two work pieces assembled by a seam with the tail pieces
of needle and hook threads on the bottom side of the work pieces; and
Fig. 7 is a path-time diagram plotting the time of operation of a presser relief drive
over the length of stroke of the presser.

INVENTION
As shown in fig 1, the sewing machine seen in the drawing machine seen in the
drawing comprises a top arm 1 and a bottom base plate 2 in the form of a casing,
the two being assembled by a standard 3 to form a C-shaped casing. An arm shaft
4 is mounted in the arm 1, drivable via a belt drive 5 by a motor 6. A control box 7
is joined to the motor 6, housing a microprocessor control system 8. A needle bar
10 is driven in up and down reciprocation by the arm shaft 4 by means of a crank 9
(fig. 3 right side, 5th item from top) a needle 11 is fixed to the lower end of the
needle bar 10.
A hook 12 is disposed in the base plate 2, which is conventionally driven in rotation
about its axis, derived from the arm shaft 4. The hook 12 is provided with a thread
supply 13.
A lifting mechanism 14 (fig. 1,3) disposed in the arm 1, serving for setting the
length of stroke a of work-piece pressers (described below); a setting shaft 15
forms art of it. The setting shaft 15 (fig. 1,3) has a guiding groove 16 (fig 3) with a
crosshead 17 (fig. 3) longitudinally displaceable therein. An end of a lever 18 (fig. 3)
is pivotably mounted on the crosshead 17 (fig. 3); the other end is articulated to a
first arm 19 (fig. 3) of an elbow lever 20 (fig. 3). The elbow lever 20 is pivotably
supported on a bearing 22 (fig. 3) stationary on the machine, at the point of
intersection of its first arm 19 and its second arm 21. A tie rod 23 (fig. 3), which
engages with a cam 24 (fig. 3), acts approximately centrally on the lever 18 (fig. 3);
the cam 24 (fig. 3) is coupled with the arm shaft 4 (fig. 1,3).

The arm 1 (fig. 1,13) is provided with a presser 25 (fig 4,5, 3) which has a presser
bar 27 (fig. 3) that is vertically displaceable in as sliding bearing 26 (fig. 3) and a
presser foot 28 (3,4,5) at the bottom end of the presser bar 27 (fig. 3). By the side
of the presser 25, provision is made for a feeder 29 (fig. 3,4,5), equally having the
function of a presser and including a feed bar 31 (fig. 3) which is displaceable in a
sliding bearing 30 (fig. 3) and to the bottom end of which is fixed a feeder foot 32
(fig. 3,5). The sliding bearing 30 (fig. 3), and thus the feeder 29 (fig. 3), are
mounted on a swing frame 33 (fig. 3) where also the needle bar 10 is lodged for
displacement in another sliding bearing 34 ( fig. 3) the feeder bar 31 (fig. 3) and
the needle bar 10 (fig. 3) being paralled to one another. The swing frame 33 (fig.
3) is pivotably mounted on a bearing 35 (fig. 3) in the arm 1 (fig. 1,3), driven by a
sliding gear transmission via a tie rod 36 (fig. 3) that is pivotably joined to the swing
frame 33 via a bearing 37 (fig. 3). A sliding gear transmission of this type is known
from DE34 23 843 C2 (corresponding to U.S. patent 4 616 586).
Actuation of the presser 25 (fig. 3.4.5) and feeder 29 (fig. 4,5) take place from the
elbow lever 20 (fig. 3), the second arm 21 (fig. 3) of which is articulated toa
traingualr driving lever 38(fig. 3), the second arm 21 being joined to a tip of the
driving lever 38 (fig. 3) by way of a tie rod 21a (fig. 3). Transmission levers 39, 40
are articulated to the two other tips; they are articulated to the upper ends of the
presser bar 27 (fig. 3) and the feeder bar 31 (fig. 3), respectively. The driving lever
38 pivotably supports itself via a rod 41 (fig. 3) on a bearing 42 (fig. 3) which
disposed in the arm 1 (fig. 1,3). The rod 41 (fig. 3) is loaded by a pre-stressed
helical compression spring 43 (fig. 3) so that the rod 41 (fig. 3) and thus the
presser 25 (fig. 3) the feeder 29 (fig. 3) are forced downwards. Disposed
underneath the rod 41 (fig. 3) is a stop lever 44 (fig. 3) which is also pivotable in
the bearing 42 (fig. 3) , having a stop 45 that is allocated to the rod 41 underneath
the compression spring 43 (fig. 3). A stop setting drive 46 in the form of a
pneumatically actuated piston cylinder drive acts on the stop lever 44 (fig. 3), its

piston rod 47 (fig. 3) being articulated to the stop lever 44 (fig. 3) while its
cylinder 48 (fig. 3) is joined to the standard 3(fig. 3) . the drive 46 (fig. 3) is a
unilaterally actuated piston cylinder drive i.e., a piston 49 (fig. 3) is mounted on
the piston rod 47 (fig. 3), with compressed air being admitted via a compressed-air
piping 50 (fig. 3) to the side of the piston 49 that faces away from the piston rod 47
(fig, 3) so that upon admission of compressed air the piston rod 47 (fig. 3) is
pushed out of the cylinder 48 (fig. 3), whereby the stop 45 (fig. 3) is adjusted
towards the stop lever 44 (fig. 3). Upon pressure relief, the piston 49 (fig. 3) and
thus the piston rod 47 (fig. 3) are restored by means of a readjusting spring 51 (fig.
3). Actuation by compressed air is controlled by a 3/2-port directional control valve
52 (fig. 3) to which compressed air is supplied from a source of compressed air (not
shown) via compressed-air supply piping 53 (fig. 3). On the other hand it is
operated electromagneticlly, to which end it is connected to the control system 8
(fig. 3) via an electric line 54 (fig. 3
The setting shaft 15 (fig. 3) for the presser 25 (fig. 3) is provided with a working
lever 55 (fig. 3), by means of which to pivot the setting shaft 15 (fig. 3) about its
axis, changing the position of the corsshead-17 guiding groove 16 (fig. 3). The
working lever 55 (fig. 3) serves to fix the length of stroke a of the presser 25 (fig. 3)
and the feeder 29. The smallest and greatest adjustable length of stroke a is
defined by two adjustable limit stops 56, 57 (fig. 3) which are which are mounted
on the arm 1 (fig. 1,3) and between which acts a lever 58 that is mounted on the
setting shaft 15 (fig. 3) . For example, 2.0 mm ≤ a ≤ 8.0 mm applies.
A rotary potentiometer 59 (fig. 3) is coupled with the setting shaft 15, visa a signal
line 60 signalling, to the control system 8 (fig. 3), the position of angle rotation of
the setting shaft 15 (fig. 3) as a measured variable.

The arm 1 (fig. 1,3) includes a needle-thread supply 61 (fig. 3), which is illustrated
only in Fig. 4. From this supply61 (fig. 3), the needle thread 62 (fig. 3) is
conventionally led via a thread tightener 63 (fig. 3), a thread lever 64 and a thread
clamp 65 (fig. 3) to the needle 11 (fig. 3). The thread tightener 63 (fig. 3) is
described in DE 28 09 848 C2 (corresponding to U.S. patent 4 289 087). It
comprises two tension disks 68, with the needle thread 62 passing there -between,
and a solenoid 67. Corresponding to the voltage fed to the solenoid 67 (fig. 3),
adjustable frictional force is exercised on the needle thread 62 (fig. 3) between the
tension disks 66 (fig. 3), conferring a corresponding tension to the thread.
The thread clamp 65 (fig. 3), which is directly upstream of the needle 11 (fig. 3),
comprises a tension disk 68 (fig. 3) fixed to a guide bar 69 (fig. 3) that is again
loaded by a compression spring 70 (fig. 3), whereby the tension disk 68 (fig. 3) is
forced against an abutment 71 (fig. 3) that is fastened to the arm 1 (fig. 3).
Provided on the abutment 71 (fig. 3) is a solenoid 71 (fig. 3) formed by wire
winding 72 (fig. 3) which can be triggered via a line 73 (fig. 3) from the control
system 8 (fig. 3).
For a sewing job, two work pieces 74, 75 are passed one on top of the other on to
the needle plate 76 (fig. 3) that is provided on the base plate 2 (fig. 3). The needle
plate 76 (fig. 3) has a recess which a bottom feeder 77 (fig. 3) projects through,
having a stitch hole 77 (fig. 3) a for the needle 11 to pass through. The bottom
feeder 77 (fig. 3) is kinematically linked to the mentioned sliding gear transmission
such that the stitch hole 77 (fig. 3) a is moved synchronously with the needle 11
(fig. 3) stitching into the work pieces 74, 75 (fig. 3) during stitch formatiion and
equally performing the feed motion. The described design and mode of operation
are familiar general practice in so-called needle-feed sewing machines.

The two work pieces 74, 75 have a total thickness s. The length a by which
the feet 28, 32 are lifted above the work pieces 74, 75 is set by an operator
by means of the working lever 55. Assumably the operator increases the
length of stroke a as the thickness s of the work pieces 74, 75 grows, the
compressibility of the two work pieces 74, 75 increasing as the thickness s
increases.
In a standard sewing operation, the needle 11, together with the needle
thread 62, passes through the work pieces 74, 75 into the stitch hole 77a.
The feeder foot 32 is in a lowered and the feeder 77 in an elevated position
so that the work pieces 74, 75 are clamped between the feeder 77 and the
feeder foot 32. At this time the presser foot 28 is above the work piece 74
corresponding to the length of stroke a so that unimpeded feed of the work
pieces 74, 75, with the needle 11 passed there-through, is possible in the
direction of feed 82. The thread clamp 65 is opened so that the needle
thread 62 can be supplied unimpeded by the downward motion of the nee-
dle 11.
When the needle 11, after passing through its lowermost position, has again
moved upwards by approximately 2.5 mm, the tip 79 of the rotating hook
12 seizes the needle-thread loop 78 formed upon upward motion of the
needle 11. With the upward motion proceeding, the needle 11 finally re-
tracts from the work pieces 74, 75. Meanwhile the hook 12 has caused the
needle thread loop 78 to entirely surround the hook-thread supply 13. Then
the excess needle thread 62 is retracted by the thread lever 64 with a two-
thread lock-stitch seam 81 forming. Afterwards the presser foot 28 and the
feeder foot 32 are shifted so that the presser foot 28 is placed on the work
pieces 74, 75 and the feeder foot 32 is lifted off by the length of stroke a.
During a standard sewing operation, the thread clamp 65 only serves as a

guide of the needle thread 62, not braking it. The described way of stitch
forming and the mode of alternating operation of the feet 28, 32 with nee-
dle feed are familiar and general practice.
When a first stitch of a seam 81 is to be sewn, the free end 83 of the needle
thread 62 i.e., the needle-thread starting end, is above the work pieces 74,
75; it is clamped between the upper work piece 75 and the presser foot 28
by a force that depends on the pre-load of the compression spring 43. For
this free end 83 to be pulled downwards through the work pieces 74, 75
when the needle-thread loop 78 is extended upon corresponding revolution
of the hook tip 79, the presser foot 28 must be relieved while the needle-
thread loop 78 is extended. This is effected by corresponding actuation of
the stop setting drive 46 by compressed air, whereby the stop lever 44 and
the stop 45 are elevated, bearing against the rod 41. In doing so, the trian-
gular driving lever 38 is slightly pivoted, as a result of which the presser
bar 27 and thus the presser foot 28 are slightly lifted without the presser
foot 28 being removed from the work pieces 74, 75, which implies pressure
relief of the work pieces 74, 75 and, consequently, reduction of the fric-
tional force that impedes the free end 83 of the needle thread 62 in being
pulled out. The accompanying downward motion of the feeder foot 32 is of
no importance functionally, the foot 32 not coming in touch with the work
pieces 74, 75. As can be seen from the above, the stop setting drive 46 is a
presser-25-relief drive. Relieving the feeder foot 32 for the free end 83 of
the needle thread 62 to be pulled to the bottom side of the work piece 75 is
in principle known from DE 36 04 299 C2 (corresponding to U.S.
4 658 752).
The distance b of the stop 45 from the rod 41 grows as the thickness s of
the work pieces 74, 75 increases i.e., the idle stroke from when the piston

rod 47 starts extending to the moment when the stop 45 bears against the
rod 41, increases as work-piece thickness s increases. For this to be com-
pensated, the time of activation of the stop setting drive 46 is increased as
the length of stroke a increases, which takes place in accordance with an
empirically determined function roughly outlined in Fig. 7, where the ac-
tuation time t is plotted above the length of stroke a. This function is re-
corded in a ROM 84 of the control system 8. The length of stroke a is
passed to the control system 8 by the rotary potentiometer 59 upon corre-
sponding adjustment of the setting shaft 15, there setting off the valve 52,
and thus the drive 46, to be triggered in accordance with the function
t = f (a). The greater the work piece thickness s, the greater is the length of
stroke a - as outlined above. Any increase in length of stroke a is accom-
panied with an increase in the duration of triggering of the stop setting
drive 46, which compensates the time loss during idle stroke over the
length b. Moreover the compressibility of the work pieces 74, 75, which
increases as the thickness s of the work pieces 74, 75 grows, is balanced.

WE CLAIM
1. A method of pulling a free end (83) of a needle thread (62) from a top of a
bottom side of at least one work piece (74, 75) upon a first stitch of a seam
(81) that is to be sewn by a sewing machine, comprising
- a needle (11) which is movable in up and down reciprocation, guiding a needle
thread (62) that has been taken from a needle-thread supply (61) by a thread
lever (64);
- at least one presser (25) to be placed on, and lifted off, the at lease one work
piece (74, 75); and
- a rotarily drivable hook (12), a tip (79) of which seizes a needle-thread loop
(78) and extends it for forming a stitch,
- with the needle thread (62) being held tight between the needle (11) and the
thread lever (64) while the needle-thread loop (78) is
- extended so that a free end (83) is pulled through the work piece (74, 75) by
the hook tip (79), and
- with the presser (25) being at least partially relieved while the needle thread
(62) is held tight; wherein as the at least one work piece (74, 75) increases in
thickness (s), the relief time (t) rises.
2. A method as claimed in claim 1, wherein relief takes place in dependence on
the length of stroke (a) of the at least one presser (25).
3. A sewing machine for putting into practice the method as claimed in one of
claims 1 or 2, comprising
- a needle (11) which is movable in up and down reciprocation, guiding a needle
thread (62) that has been taken from a needle-thread supply (61) by a thread
lever (64);

- at least one presser (25) to be placed on, the lifted off, the at least one work
piece (74, 75); and
- a rotarily drivable hook (12), the tip (79) of which seizes a needle-thread loop
(78) and extends it for forming a stitch,
- a needle-thread-(62) clamp (65) which is stationarily provided between the
thread lever (64) and the needle (11).
- a presser drive; and
- a control system (8) for the thread clam (65) and the presser drive; wherein a
presser-relief drive is triggered by the control system (8) in accordance with a
function which is recorded in the control system (8), reflecting the dependency
of the time of actuation of the presser-relief drive on the thickness (s) of the at
least one work piece (74, 75).
4. A sewing machine as claimed in claim 3, wherein a feeder (29) is provided,
which is drivable alternately of the presser (25); a joint drive is provided for the
presser (25) and the feeder (29); and the presser-relief drive is a presser-lift -
off drive (46).
5. A sewing machine as claimed in claim 4, wherein an adjustable lifting
mechanism (14) is provided for adjustment of the length of stroke (a) of the
presser (25); and a potentiometer (59), which is coupled with the lifting
mechanism (14), is provided for detection and transmission, to the control
system (8),

of a measured variable representing the length of stroke (a) of the presser
(25) which is adjusted on the lifting mechanism (14).

In a method of pulling the free end (83) of the needle thread (62) from the top of
the bottom of at least one work piece (74, 75) upon a first stitch of a seam (81)
that is to be sewn, use is made of a sewing machine with at least one presser (25)
which can be placed on, and lifted off, the work piece (74, 75). The needle thread
(62) is held tight while a needle-thread loop (78) is extended by the tip of the
hook (13) so that the free end (83) is pulled through the work piece (74, 75).
While the needle thread (62) is held tight, the presser (25) is at least partially
relieved. The relief time increases as the thickness (s) of the work piece (74, 75)
grows.

Documents:

381-kol-2003-granted-abstract.pdf

381-kol-2003-granted-claims.pdf

381-kol-2003-granted-correspondence.pdf

381-kol-2003-granted-description (complete).pdf

381-kol-2003-granted-drawings.pdf

381-kol-2003-granted-examination report.pdf

381-kol-2003-granted-form 1.pdf

381-kol-2003-granted-form 18.pdf

381-kol-2003-granted-form 2.pdf

381-kol-2003-granted-form 3.pdf

381-kol-2003-granted-form 5.pdf

381-kol-2003-granted-pa.pdf

381-kol-2003-granted-priority document.pdf

381-kol-2003-granted-reply to examination report.pdf

381-kol-2003-granted-specification.pdf

381-kol-2003-granted-translated copy of priority document.pdf

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Patent Number

227771

Indian Patent Application Number

381/KOL/2003

PG Journal Number

04/2009

Publication Date

23-Jan-2009

Grant Date

20-Jan-2009

Date of Filing

09-Jul-2003

Name of Patentee

DURKOPP ADLER AKTIENGESELLSCHAFT

Applicant Address

POTSDAMER STRASSE 190, D-33719 BIELEFELD

Inventors:

#	Inventor's Name	Inventor's Address
1	ENNS JOHANN	REICHENBACHER STRASSE 5, D-33813 OERLINGHAUSEN
2	HOSAGASI SEVKI	RUMBECKER STRASSE 10, D-33699 BIELEFELD

PCT International Classification Number

D05B 47/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10234251.2	2002-07-27	Germany