Abstract:
A method for cutting the lower and at least one upper thread for lead-in embroidering or lead-in sewing is performed with a device including thread catchers ( 19   a - 19   c ) connected with each other in a fixed manner and layered over top of each other, formed of sheet metal, as well as spring and thread tightening plates ( 31  and  41 ) arranged above and below the thread catchers, which move back and forth against a blade ( 29 ), and a thread wiper unit. The device is exclusively operated by a drive moving back and forth and driving the thread cutting and lead-in stitching unit ( 5 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Swiss Patent Application No. 00339/11, filed Feb. 28, 2011, which is incorporated herein by reference as if fully set forth. 
     BACKGROUND 
     The invention is directed to a method for cutting the lower and at least one upper thread at the end of a sewing or embroidering process, a method for lead-in stitching at the beginning of a sewing or embroidering process, as well as a device for performing these methods. 
     A flawless beginning of a sewing or embroidering stitching always requires that the upper and the lower thread exhibit a suitable length and, if possible, position in reference to the sewing or embroidering material. This condition is usually not given, though, when a sewing or embroidering process is ended in the usual fashion. When the threads are not located in a defined good position no optimal first stitch and/or first knot is achieved. This can lead to problems in further processing of the sewing or embroidering material, and particularly it is undesirable for esthetic and functional aspects. 
     SUMMARY 
     One objective of the present invention comprises providing a method and a device for a sewing machine with a CB-hook (central bobbin-hook) like device or a CB-hook, which allows at the end of a sewing or embroidering process the cutting-off of the upper and the lower thread at a desired length and provides the loose ends of the upper and the lower thread at the machine in an optimal position for lead-in stitching and/or sewing. Another objective of the invention comprises providing a device for implementing such a method. 
     These objectives are attained in the methods as well as the device according to the invention. 
     These objectives are flawlessly attained in a displacement of the upper and the lower thread perpendicularly in reference to the axis of the needle during the stitch formation and by a temporary holding and/or braking of the upper thread underneath the stitching plate. The use of the thread cutting and/or lead-in stitching unit according to the invention allows performing the processing steps without any additional thread tensioning or thread clamping system or any inversing of the rotary direction of the machine and/or its primary shaft. The thread cutting and lead-in stitching unit holds the loose thread(s) until the second stitch and allows a tight knot in the material. The drive of this unit occurs by coupling it via a stroke magnet to the primary drive train, which magnet acts as an actuator. A mandatorily guided cam drive provides the required kinematics. The differentiation if the thread cutting function or the lead-in stitching function is to be performed occurs exclusively via the electrification of a stroke magnet, dependent on the upper shaft, at the respectively predetermined rotary angle of the primary shaft. It is advantageously achieved to increase the cutting speed or to reduce the cutting time and to obtain a high lead-in stitching quality. Here, the risk of the thread jamming in the hook path can be minimized. Additionally, any lateral displacement of the needle is not required for and/or during the thread cutting function. Furthermore, the method according to the invention allows thread cutting the lead-in stitching with CB-hook systems and rotary hook systems. 
     The activation mechanics for performing the thread cutting and lead-in stitching functions comprise a very simple design and includes a number of plates located over top of each other with different configurations and ends specifically embodied for said functions. Some of these plates are jointly pushed forward and backward by a linearly acting drive and, in order to bring the thread ends into an optimal position, engage additional stationary arranged plates with suitable recesses for a temporary deflection and/or clamping of the threads, depending on the feed position. The drive of the activation mechanism can be triggered directly via the upper shaft and occur with the cam mechanics on the primary shaft synchronously in reference to the rotary angle of the two shafts. 
     Alternatively, the drive can be performed by a servomotor or a stepper motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail using illustrated exemplary embodiments. Shown are: 
         FIG. 1  is a perspective, sectional illustration of the stitching plate and the hook located underneath thereof as well as a thread cutting and lead-in stitching mechanism at the beginning of the first stitch, upper shaft position 220°, 
         FIG. 2  is a view of an arrangement similar to  FIG. 1  after a rotation of the upper shaft by 50°, a thread catcher begins to move in the x-direction and grasps the lower thread with a lower thread-catching edge, 
         FIG. 3  is a view with a rotary angle of 290°; the lower thread is ejected by the lower thread edge and held in a thread receiver; the needle pierces into the material, 
         FIG. 4  is a view of the arrangement at 320°, the thread catcher reaches its end position, the lower thread is maximally deflected, 
         FIG. 5  is a view of the arrangement after a rotation of 190° at 50°, the hook tip engages the upper thread, 
         FIG. 6  is a view of the needle thread and the material thread being spread (80°), 
         FIG. 7  is a view at 110°, the needle and material thread are maximally spread, the thread catcher begins to move in the x-direction, 
         FIG. 8  is a view of the arrangement at 140°, the thread catcher engages the needle and the material threads with separate catching contours, 
         FIG. 9  is a view at 175°, the needle thread is pulled forward by the thread lever into the required length and the upper thread and the lower thread are in a position shortly before being severed, 
         FIG. 10  is a perspective view of the free cutting arrangement, comprising several plates located over top and displaceable in reference to each other, 
         FIG. 11  is an enlarged perspective view of the cutting device in  FIG. 10  in the severing moment (the lower thread is shown), 
         FIG. 12  is a view similar to  FIG. 11 , immediately after cutting, 
         FIG. 13  is a view at 185°, the thread catcher reaches its initial position, the upper thread is pulled by the thread lever out of the thread catching mechanism, the lower thread is located in a defined position on the thread guiding plate and is here held in its position, 
         FIG. 14  is a view at 220°, the first cycle is concluded, at least one upper and the lower thread are separated and pulled forward to the required length, ready for stitching or lead-in embroidering, the machine stops, a new work piece can be inserted, 
         FIG. 15  is a view as the machine begins to generate the first stitch at an upper shaft angle of 220°, 
         FIG. 16  is a view at 30°, the upper thread-loop has been created and the hook engages the upper thread-loop, 
         FIG. 17  is a view at 60°, the thread catcher beings to shift towards the right, 
         FIG. 18  is a view at 80°, the upper thread-loop engages the material thread as well as the needle thread at the thread catcher in the recesses arranged appropriately, 
         FIG. 19  is a view at 90°, the material thread has been pulled by the thread catcher under the stitching plate, 
         FIG. 20  is an enlarged section view from  FIG. 19 , 
         FIG. 21  is a view at 95°, the thread braking plate is opened by the thread catching unit at the site marked A and the thread wiper is operated by the central thread catcher, 
         FIG. 22  is a view at 100°, the thread brake plate briefly closes (the threads are located equivalent to the arrangement in  FIG. 21 ), 
         FIG. 23  is a view at 120°, the thread lever reaches the end position and pulls the existing thread through the opened low-friction thread braking plate to the desired length, the first stitch is completed, 
         FIG. 24  is a view at 240°, the second stitch begins and the thread braking plate closes briefly and acts as a temporary thread brake, which is impinged to an increased force, 
         FIG. 25  is a view at 255°, the thread catcher is returned into its initial position and the upper thread is now retained by the thread braking plate with a defined holding force, a tight knot forms, and the thread wiper wipes at least one upper thread and the lower thread into a defined position, 
         FIG. 26  is a view at 265°, equivalent to an enlarged illustration of a section of  FIG. 25 , 
         FIG. 27  is a view at 30°, the second stitch is generated, 
         FIG. 28  is a view at 50°, the hook pulls the thread loop away from the needle, 
         FIG. 29  is a view at 150°, the thread lever pulls back the upper thread, 
         FIG. 30  is a view at 170°, the needle thread is located slightly below the stitching plate, 
         FIG. 31  is a view at 190°, the lower thread is engaged by the upper thread and the thread lever pulls the knot to the underside of the material, and 
         FIG. 32  is a view at 220°, the thread lever has pulled the upper thread-loop with the engaged lower thread to the underside of the material and a tight knot is completed, 
         FIG. 33   a  is an enlarged view of the thread cutting and lead-in stitching unit in the initial position, 
         FIG. 33   b  is an enlarged view of the thread cutting and lead-in stitching unit in the initial position, however in the end position, 
         FIG. 33   c  is a detailed view of the thread cutting unit from the top after catching the upper thread, 
         FIG. 33   d  is a view of the thread cutting unit after another step, 
         FIG. 33   e  is a view of the thread cutting unit after another step, thread in the thread receiver, 
         FIG. 34  is an exploded illustration of the thread cutting and lead-in stitching device, 
         FIG. 34   a  is a view showing one situation of the thread position, 
         FIG. 35  is a perspective view of the thread wiper and thread braking unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the illustration according to  FIG. 1  a hook is marked with the reference character  1  and a stitching plate with the reference character  3 . A thread cutting and lead-in stitching unit  5  is discernible between the hook  1  and the stitching plate  3 . The thread cutting unit  5  comprises a multitude of movable plates, located over top of each other, partially arranged fixed and partially in a manner movable synchronously in reference to each other, serving as thread catchers and thread deflectors and redirectors (in  FIG. 10  shown in an exploded illustration). The description and/or functions of the individual plates occur partially in the individual processing steps, shown in the following figures. 
       FIG. 1  shows the initial position of the thread cutting unit  5  and none of the plates engages any of the threads (upper thread  7  or lower thread  9 ). The performance of the last stitch at the end of a sewing or embroidering stitching is described based on  FIGS. 1 through 14 . It is assumed that the upper thread  7  and the lower thread  9  are essentially located in the position shown in  FIG. 1  and form a stitching. At the beginning of the last stitch at an angle of the upper shaft of 220° the last stitch begins and the needle  11  holds the upper thread between the stitching hole  13  stretched essentially in a straight line; the lower thread  9  extends essentially straight from its exit from the bobbin case  15  towards the stitching hole  13 . Now a synchronous shifting starts of the three thread catching plates, i.e. the upper, central, and lower thread catchers  19   a ,  19   b , and  19   c  for short, a thread stretching plate  31 , and a clamping plate  61 . At an upper shaft angle of 270°, i.e. after a rotation by 50°, the control edges  17   a ,  17   b  engage the upper thread catcher  19   a  and the central thread catcher  19   b , i.e. the plates of the thread cutting unit  5 , the lower thread  9  ( FIG. 2  and  FIG. 33   c ). After another angular rotation of 20°, i.e. at an angle of the upper shaft of 290°, using their control and separating edges  17   a ,  17   b , the upper thread catcher  19   a  and the central thread catcher  19   b  have deflected the lower thread  9  after ejection towards the right in  FIG. 3  and in detail in the  FIGS. 33   d  and  33   e . In these positions the lower thread  9  is ejected from the control edges  17   a ,  17   b  and glides into a thread receiver  21  in a stationary thread guiding plate  33 . 
     At an upper shaft angle of 320° the tip of the needle  11  has crossed the stitching plate  3  and after another 50° the hook tip  23  has engaged the upper thread loop  25  and deflected the upper thread  7  towards the left between the stitching hole  13  and the hook tip  23  ( FIG. 5 ). After another 30°, i.e. at an angle of the upper shaft of 80° the needle  7  has already left the stitching plate  3  towards the top and the upper thread loop  25  is further spread apart by the edges  17   e  and  17   d  of the thread catcher  19   a  and  19   b . After another 30°, i.e. at an angle of the upper shaft of 110°, the upper thread loop  25  is spread almost completely. The needle thread  7   a  is engaged by the edge  17   c . Simultaneously the upper and the central thread catchers  19   a  and  19   b  pull the lower thread  9  between the stitching hole  13  and the thread receiver  21  towards the left, so that it extends between the stitching hole  13  and the thread catcher  19   a  approximately in the direction of the needle  11  ( FIG. 7 ). 
     In  FIG. 8  the upper thread loop  25  has passed below the nadir of the hook  1  and is located in the ejection position. The lower thread  9  is deflected further to the left by the continued retracting thread catchers  19   a ,  19   b  and now extends above the upper thread catcher  19   a  at an acute angle in reference to the stitching hole  13 . Simultaneously the needle thread  7   a  is braked and/or decoupled ( FIG. 34   d ) and the thread tension (tensile organ not shown) is opened so that the needle thread  7   a  can be pulled forward by the thread lever out of the thread bobbin to the required length ( FIG. 8 ). 
     At an angle of the upper shaft of 175° the material thread  7   b  of the upper thread  7  and the lower thread  9  are cut and/or severed ( FIG. 9 ). 
     The cutting occurs as shown in  FIG. 11  for the lower thread  9  by the lower and the upper thread  7  being held at the position A in the thread guide plate  33  and is pulled at the position B over a fixed arranged blade  29  and cut. Using the spring blade  31  the lower thread  9  is braked before it is cut. Prior thereto, the steps occurred that at an angle of the upper shaft of approximately 175° the upper thread  7  to be cut was pulled towards the blade  29  by the edges  17   a ,  17   b ,  17   c  at the thread catchers  19   a ,  19   b ,  19   c , i.e. towards the left, to reach the required length ( FIG. 11 ). This (occurs) without any increase in tension upon the upper thread  7  in order to avoid negatively influencing the already sewn seam. Shortly before the stationary fastened blade  29  is reached, a thread tension is impinged locally upon the thread  7  to be cut by the spring blade  31  at the thread cutting unit  5  (see  FIGS. 10 and 34 ), its frontal edge  32  acting as the spring. Now, the upper thread  7  and the lower thread  9  can be pulled as “stationary loops” through the blade  29  and securely cut here ( FIG. 12 ). 
     After another rotation of the upper shaft to an angle of 185° the thread catchers  19  have reached their initial position. The upper thread  7  is pulled by the thread lever (not shown) out of the thread catchers  19 . Now the lower thread  9  is located in the defined position C ( FIG. 12 ) on the thread guide plate  33  and is held here in its position. 
     At an angle of the upper shaft of 220° the cycle is concluded. The sewing foot (not shown) is raised and the material to be sewn (not shown) can be removed. The upper thread  7  and the lower thread  9  are separated from the material and pulled forward to the required length ( FIG. 14 ). 
     Contrary to the angle of the upper shaft of 220° at the beginning of the last stitch at the end of a seam now the upper thread  7  and the lower thread  9  are no longer stretched from the needle  11  to the stitching hole  13  and/or from the bobbin case  15  to the stitching hole  13 . At least one upper thread  7  is loose and the lower thread  9  is positioned by the thread cutting unit  5 . They are now located in an optimal starting position for the lead-in embroidering and/or sewing of a new seam. 
     Through the use of the thread cutting and lead-in stitching unit  5  both the upper thread  7  as well as the lower thread  9  are located at the end of a sewing or embroidering seam in an optimal position for lead-in stitching (cf.  FIG. 15 ) a new lead-in embroidering or sewing occurs at an angle of the upper shaft of 220°. As discernible from  FIGS. 14 and 15  a loop  63  is formed in the lower thread  9 , which extends from the exit of the lower thread  9  out of the bobbin case  15  towards the right and therefrom back in the direction towards the stitching hole  13 . The loop  63  is now positioned, but not held. After the needle has pierced the material at an angle of the upper shaft of 30° the hook  1  has engaged the upper thread loop; here, the loop  63  of the lower thread  9  has not been changed. At an angle of the upper shaft of 60° ( FIG. 17 ) the upper thread loop is guided counter-clockwise towards the left around the hook  1  and the thread cutting and lead-in stitching unit  5  moves according to a predetermined motion process towards the right, driven by the primary shaft or by a motor. After further rotation of the upper shaft by 20° ( FIG. 18 ) the loose material thread  7   b  of the upper thread  7  is engaged by the recesses  45  and the needle thread  7   a  of the upper thread  7  by respective recesses or slots at the thread catchers  19   a ,  19   b ,  19   c , with the free end of the material thread  7   b  being pulled underneath the stitching plate  3 .  FIG. 19  now shows the material thread underneath the stitching plate  3  and in an enlarged illustration in  FIG. 20  it is clearly discernible how the material thread  7   b  (top) and the needle thread  7   a  (bottom) are guided at a distance from the lower thread catcher  19   c . After another rotation of the upper shaft by approx. 5° a thread braking plate  65  ( FIG. 35 ) has been opened by the thread catcher  19  ( FIG. 17   f ,  FIG. 34 ) and according to  FIG. 22  the thread braking plate  65  briefly closes at an angle of the upper thread of 100°. The position of the threads is unchanged with regards to the angle of the upper thread of 95°. 
     At an angle of the upper thread of 120° a temporary end position has been reached and the thread braking plate  65  is opened again. The thread lever pulls the existing upper thread  7  through the opened low-friction thread braking plate to the required length. At an angle of upper shaft of 240°, i.e. after the completion of an entire machine rotation by 360°, the thread braking plate  65  briefly closes. This provides additional important process security because the loose upper thread  7  cannot be entrained by the thread catcher  19  (position D) out of the thread braking plate  65 . At 255° the thread catchers  19   a - 19   c  return into the initial position and the upper thread  7  is retained by a defined holding force in order to allow the formation of a tight knot and additionally the loose upper thread loop cannot be pulled through the hole in the material ( FIGS. 25 and 26 ). In  FIG. 27  it is discernible how the stitch is generated; this at an angle of the upper shaft of 25°. At an angle of the upper shaft of 50° the hook  1  pulls the upper thread  7  of the following (second) stitch away from the needle  11  ( FIG. 28 ) and at 150° the lower thread  9  is engaged by the upper thread  7  and the thread lever pulls the knot in the direction towards the underside of the material ( FIG. 29 ). After another rotation of the upper shaft by 20° the thread lever has engaged the upper thread loop with the engaged lower thread loop pulled to the underside of the material and the desired tight knot is realized. 
     At 200° the lead-in stitching function is successfully concluded after two stitches and the next stitches can occur. In turn,  FIGS. 33   a  and  33   b  essentially show the thread cutting unit  5 , as already shown in  FIG. 1 , however in an enlarged scale and additionally the wiper unit and the thread braking unit  37  are integrated in addition to the already described thread catchers  19   a - 19   c  and the thread guide plate  33 , once more illustrated in  FIG. 35  in an enlarge fashion. 
     In  FIGS. 33   c, d , and  e  it is shown enlarged how the thread reaches the thread receiver  21 . The reference character  45   a  marks a thread contour at the thread catcher  19   a  and the contour  45   b  at the thread catchers  19   b  is not active in  FIG. 33 . However, according to  FIG. 33   e  the thread is guided from the two v-shaped contours  47   a  and  47   b  at the frontal ends of the thread catchers  19   a  and  19   b  via the contour  47   c  at the thread catcher  19   c  into the thread receiver  21 . All transfers of the thread occur by the displacement of the elements  19   a - 19   c  as well as  31  and  61  of the thread cutting unit  5  in reference to the elements of the wiper and thread braking unit  37  arranged fixed at the sewing machine. Only a linear displacement according to a predetermined speed progression occurs. Only the wiper and thread braking unit  37 , with the wiper lever  51  and the thread braking plate mounted thereat, performs a motion laterally extending in reference to the direction of feed of the thread cutting unit  5 , which is triggered by the guiding edge  17   g  at the central thread catching plate  19   b . The wiper unit  37  is locally fixed arranged in the lower arm of the sewing machine. Two pivotal and spring-loaded levers are arranged on the wiper and thread braking unit  37 , namely the thread braking plate  65  and a wiper lever  51 . For this purpose, the two-arm wiper lever  51  carries on the first of its arms a pin  53  located parallel in reference to the rotary axis of the wiper lever  51 , which is pushed laterally by the lower thread catcher  19   c  (contour  17   f ). When pivoting the wiper lever  51  the cut-off ends of the threads are pushed sideways and then rest in an optimal lead-in embroidering and/or sewing position. 
       FIGS. 33   a  and  33   b  once more show the mutual arrangement of the thread catchers  19   a - 19   c  as well as the spring blade  31  in reference to the fixed arranged thread wiper unit  37  in the resting position.  FIG. 33   b  shows the thread catchers  19   a - 19   c  as well as the spring blade  31  and the thread guide plate  33 , which are mutually connected to each other, moved towards the right and considerably more intersecting the thread wiper unit  37 .  FIGS. 33   c - 33   e  shows the position of the thread during the different phases. 
     For a better understanding,  FIG. 24  shows the parts of the thread cutting unit  5  in an exploded illustration. 
     LEGEND OF REFERENCE CHARACTERS 
       1  hook 
       3  stitching plate 
       5  thread cutting unit 
       7  upper thread 
       9  lower thread 
       11  needle 
       13  stitching hole 
       15  bobbin case 
       17  control edge and separating edge 
       19  first thread catcher, lower thread catcher 
       21  thread receiver 
       23  hook tip 
       25  upper thread loop 
       27  second thread catcher, upper thread catcher 
       29  blade 
       31  spring blade 
       32  front edge of  31   
       33  thread guide plate 
       35  second thread catcher 
       37  wiper and thread braking unit 
       39  thread catcher 
       41  thread tension plate 
       43  clamping plate 
       45  slot 
       47  slot 
       51  wiper lever 
       53  pin 
       55  second arm 
       59  ejection edge (lower thread) 
       61  clamping plate 
       63  loop 
       65  thread braking plate